Group winners automatically qualify for the finals, the eight best runners-up go into two-legged playoffs.
Croatia could only draw 1-1 in Serbia, so Belgium's 2-0 win in Scotland has put Marc Wilmots' team on the verge of their first World Cup finals since 2002.
Belgium lead Croatia by five points with two games left to play. When the two teams meet in Zagreb next month, a draw will take the Lowlands nation to Brazil. Croatia have to win that game and then hope that results go their way on the final day -- when they travel to Scotland and Belgium host Wales.
Italy moved a step closer to the World Cup finals with a 1-0 win over Bulgaria and will secure their place with a victory over the Czech Republic in Turin on Tuesday.
Friday's results have blown the race for the second spot wide open, with four nations in the hunt. Bulgaria, the only one of the contenders that do not have to play Italy, are in pole position with 10 points. Czech Republic missed the chance to go second by suffering an injury-time loss at home to Armenia, while Denmark edged out Malta 2-1.
With Bulgaria, Czech Republic, Armenia and Denmark all separated by just one point and with three fixtures to play, it is too close to call. Armenia must do it the hard way as they are the only one of the four nations that do not meet bottom-of-the-table Malta.
Germany beat Austria 3-0 and will qualify for the World Cup on Tuesday if they complete a routine win in the Faroe Islands and Sweden fail to win in Kazakhstan.
The real battle is for second. Sweden claimed a massive comeback win in the Republic of Ireland on Friday to move three points clear in second with three games to go. The Swedes hold a three-point lead over Austria and Ireland, but with Sweden to play Austria and Germany in their final two fixtures, they still have plenty of work to do.
Austria and Ireland meet in Vienna on Tuesday. Whoever loses that match will effectively be out of the running for the playoffs. A draw would be the perfect result for Sweden.
Although Netherlands suffered a shock 2-2 draw in Estonia, and even then needed a 94th-minute Robin van Persie penalty to avoid defeat, they remain in the box seat to win the group with a six-point lead over Romania with three games to go. Louis van Gaal can start planning for Brazil if they secure the certain win in Andorra on Tuesday and Romania fail to beat Turkey in Bucharest.
Romania's 3-0 win over Hungary on Friday moved them two points above their visitors into second, while Turkey won 5-0 over Andorra and are a point further back. Turkey are the only one of the three contenders that do not have Andorra still to play, while Romania are the only team not to face Netherlands. If Romania avoid defeat at home to Turkey on Tuesday, Victor Piturca's team will be hot favourites to take the playoff place.
Switzerland have had opportunities to wrap up this group but continue to pass up them up. After drawing 0-0 in Cyprus in the last group game in March, they led Iceland 4-1 on Friday with 34 minutes to go but threw away the win as Johann Berg Gudmundsson completed his hat trick in the 91st minute to claim an unlikely 4-4 draw.
However, Albania's 1-0 loss in Slovenia has provided much-needed breathing space, with Ottmar Hitzfeld's Swiss still enjoying a four-point cushion with three games left. Norway are their nearest challengers, and the two teams meet in Oslo on Tuesday. A Switzerland win will put one foot in the finals, while if Norway take the points, the group is wide open.
Albania and Iceland are a point adrift of Norway, with Slovenia another point back. Tuesday's matches -- the other games see Slovenia go to Cyprus and Iceland host Albania -- will shape what could promise to be a titanic battle to reach the finals next month.
Portugal may occupy the top spot on 17 points, but it is Russia two points back that are the favourites to book an automatic ticket. Russia play their game in hand at home to Israel on Tuesday, and victory will send them to the top with only Luxembourg and Azerbaijan to play.
Israel's hopes are hanging by a thread after they could manage only a 1-1 draw with Azerbaijan on Saturday. They must now win in Russia if they are to harbour any realistic hopes of making the finals.
What a difference 90 minutes has made for Bosnia-Herzegovina. Safet Susic had guided his team to a three-point lead and had already played nearest challengers Greece home and away. But a 1-0 home defeat to Slovakia, coupled with a Greece win in Liechtenstein, means the two teams are now level on points with three games to go.
Bosnia-Herzegovina's goal difference is so superior that three victories will effectively guarantee a place at the World Cup, but they have two away games to play, one of which is in Slovakia, while all of Greece's remaining fixtures are on home soil.
Slovakia can cling to slim hopes four points back, but in reality it would be a major shock if both Greece and Bosnia-Herzegovina capitulated.
Poland's 1-1 home draw with Montenegro played into the hands of England and Ukraine, who both recorded comfortable wins on Friday.
England head to Kiev as group leaders on Tuesday with the knowledge that a point could be a good result; it would leave them a point in front of both their hosts and Montenegro with two games at Wembley next month. An England win would make top spot all the safer due to their superior goal difference, but a victory for Ukraine and Roy Hodgson could be staring at the playoffs.
Montenegro, level on points with England but with one more game played, will surely have to win at Wembley to stand a realistic chance of topping the group. Poland, five points back, are not completely out of it with a game against San Marino to play, but they also must cause an upset in London to get into the shake-up.
France's shock 0-0 draw in Georgia has effectively consigned them to the playoffs. World champions Spain lead France by three points with only two games remaining, and as they do not meet, there is little chance of Didier Deschamps' team being able to close the gap. Spain would have to lose at home to Belarus or Georgia just to open the door. It is going to be the playoffs again for France.
The top three nations in the final group stage qualify directly for the finals, with the fourth-place team facing a two-legged playoff against New Zealand.
Mexico's 2-1 defeat at home to Honduras, only their second-ever loss at the Azteca in 77 World Cup qualifying matches, cost Jose Manuel "Chepo" de la Torre his job. A nation that has not failed to qualify for the World Cup since Spain '82 (they were banned for the 1990 finals) is in danger of missing out.
Costa Rica moved to the top of the qualifying group with a fine 3-1 home win over the United States, who are second and one point back. The USA host Mexico on Tuesday and will book their place at the finals with a victory, which would mean Mexico are in danger of not only facing a playoff but perhaps missing out altogether.
Costa Rica go to rock bottom Jamaica, who are without a win, and will also reach the finals with a victory if other results go their way.
Honduras, currently in the third and final automatic berth, are at home to Panama and could move to the brink of their second consecutive World Cup appearance, and only their third overall, if they take the three points. But Panama, which have picked up only one point on their travels, know a victory brings them right back into contention level on points with Honduras.
The top four nations qualify automatically from the region, and the fifth-place team plays either Jordan or Uzbekistan in a two-legged playoff.
Argentina were not in action on Friday, so it was left to Colombia and Chile to join them on the brink of qualification with wins over Ecuador and Venezuela, respectively. Chile were in South Africa in 2010, but Colombia have not reached the finals since the days of Carlos Valderrama in 1998.
Uruguay moved back into serious contention for an automatic position as two goals from Luis Suarez claimed a 2-1 win away in Peru.
Argentina (away to Paraguay) and Colombia (away to Uruguay) can book their place at the finals with wins on Tuesday. Chile are not in action and will be hoping that Uruguay are beaten by Colombia to strengthen their position. Ecuador, who travel to bottom of the table Bolivia, are currently in the final automatic berth.
Victory for Uruguay would likely leave at least four nations separated by four points going into the final two rounds next month.
Prior to this weekend's final round of group games Ivory Coast, Egypt and Algeria had already booked their places in the playoffs, with the 10 group winners meeting in two-legged ties.
Ethiopia thought they had won Group A in June only to see their 2-1 win over Botswana awarded as a 3-0 win to their opponent as they fielded Minyahil Teshome when he was suspended for receiving two yellow cards in earlier qualifiers. That meant they had to beat Central African Republic to go through, and they came from behind to win 2-1 with Teshome netting the winner. South Africa's 4-1 win over Botswana was academic.
Tunisia suffered a similar fate, having thought they had won Group B in June. However, a FIFA Disciplinary Committee decision went against them, as a 4-3 loss for Cape Verde Islands in Equatorial Guinea was reversed to a 3-0 win due to an ineligible player.
So the group went down to the final day, with Tunisia at home to Cape Verde Islands in need of a point to take the top spot for a second time. But Cape Verde won 2-0 in Rades to make the playoffs instead.
Ghana secured their place from Group D on Friday. Needing to avoid defeat at home to Zambia, they won 2-1 in Kumasi to finish four points clear of their nearest rival.
In Group E, Congo looked like the hot favourites to go through, a point clear of Burkina Faso with a trip to Niger, who had lost four of their five group games, on the final day. But with Congo drawing 2-2 in Niamey, Burkina Faso leapfrogged them to win the group courtesy of Prejuce Nakoulma's goal against Gabon.
Like Ghana, Nigeria had to avoid a home defeat to ensure they entered the playoffs. The Super Eagles navigated their home game against Malawi with little trouble, winning 2-0 in the Group F showdown in Calabar.
Senegal advanced from Group J with a 1-0 win over Uganda. Like others in the region, they just had to avoid defeat to go through, and Sadio Mane's goal in the 84th minute calmed the home side's nerves to book their passage.
The final place was decided Sunday when Group I rivals Cameroon and Libya met in Yaounde. Aurelien Chedjou scored the only goal of the game to ensure the Indomitable Lions made it into the play-offs.
Based on the current FIFA World Rankings, which may change, possible seedings for the draw would be:
Seeded: Ivory Coast, Ghana, Algeria, Nigeria, Cape Verde Islands
Unseeded: Burkina Faso, Cameroon, Egypt, Senegal, Ethiopia
With group play already completed, Iran and South Korea qualified from Group A, with Japan and Australia making Brazil from Group B.
The two third-place sides, Jordan and Uzbekistan, drew 1-1 in the first leg of their playoff on Friday. The two teams meet again in the Uzbek capital of Tashkent on Tuesday, with the winning nation meeting the fifth-place side from South America to qualify.
Qualifying was completed last year with New Zealand advancing to an intercontinental playoff against the fourth-place team from CONCACAF.