Portugal slumped to an embarrassing defeat at home to Albania in their opening Euro 2016 qualifier, while Germany needed two goals from Thomas Muller to help them see off Scotland.
Any hopes of bouncing back from a miserable World Cup were shattered for Portugal after they suffered a shock 1-0 loss to Albania.
A stunning volley from Bekim Balaj early in the second half decided the match, with the hosts -- without the rested Cristiano Ronaldo -- unable to muster a response.
The Portuguese crashed out in the group stages in Brazil and this was another setback for a team which still included a host of household names.
Scotland put up a spirited show, going down 2-1 to world champions Germany.
Thomas Muller gave the hosts a first half lead in Dortmund, only for Ikechi Anya to level midway through the second half.
However, Gordon Strachan's men were undone by Muller's second goal of the night four minutes later -- before Charlie Mulgrew was dismissed in the closing stages when he kicked the ball away and received a second yellow card.
Aiden McGeady launched Martin O'Neill's competitive reign as Republic of Ireland boss in style with a match-winning double in a 2-1 victory in Georgia.
The Republic looked likely to have to settle for a point at the Boris Paichadze Dinamo Arena in Tbilisi after Tornike Okriashvili's piledriver had cancelled out McGeady 24th-minute opener.
But with time running down, the Everton winger -- who worked under O'Neill during his time as Celtic manager -- curled home a 90th-minute winner which ensured Ireland headed back to Dublin with the opening night win upon which they had set their hearts.
McGeady turned in arguably the best performance of his international career on a night when he collected his 70th cap, and he undoubtedly made the difference between two well-matched sides in a game which see-sawed throughout.
Kyle Lafferty and Niall McGinn were the late heroes as Northern Ireland secured a dramatic 2-1 win in Hungary.
Hungary had looked set to take the points on their first outing at the new Groupama Arena when former Watford striker Tamas Priskin headed home a 74th-minute corner.
But Michael O'Neill's men ripped up the script as Lafferty's brilliant run and pass left McGinn with the simplest of tap-ins with 10 minutes to go.
The pair then swapped roles with three minutes left, McGinn ghosting into the box and crossing for Lafferty, who willed the ball over the line as he tangled with Vilmos Vanczak and somehow got the job done from the most ungainly position.
Denmark were spared another home embarrassment at the hands of Armenia as goals from Pierre Emile Hojbjerg and Thomas Kahlenberg secured the Scandinavians a come-from-behind 2-1 victory.
Playing a nation who had pulled off a famous 4-0 victory over them at Parken during World Cup qualifying in 2013, the Danes looked set to be humbled by the Armenians in Copenhagen once again when Borussia Dortmund midfielder Henrikh Mkhitaryan's strike put the away side 1-0 up in the 50th minute.
However, Hojbjerg levelled 15 minutes later with a long-range effort, and with 10 minutes of the contest to go substitute Kahlenberg headed home the winner.
Riku Riski rescued Finland from an embarrassing situation to win 3-1 against the Faroe Islands.
Finland trailed to a Christian Holst goal and were in danger of becoming the Faroes' first major scalp since June 2011.
But Riski scored a brace to spin the tie around and then Roman Eremenko added a late third for good measure.
It was the least Finland deserved after a dominant display, but they will not be the neutrals' favourite after ruining the romance of a possible Faroes' win.
Romania gained instant revenge on Greece for beating them to World Cup qualification as Ciprian Marica's penalty sealed a 1-0 win.
Marica netted from the spot after 10 minutes to give the visitors a victorious start to their Euro 2016 qualifying campaign.
The striker was later sent off, but his side held on to defeat the side who beat them in a playoff for a place in Brazil.
Gibraltar's first-ever senior competitive game ended in a 7-0 thumping by Poland.
Robert Lewandowski scored four, Kamil Grosicki fired in two and Lukas Szukala also got onto the scoresheet in a predictably one-sided match at Estadio Do Algarve.
Gibraltar, UEFA's newest member and a country with a population of around 30,000, were accepted by the European governing body in May 2013 following a 14-year battle. They face a tough test with a team predominantly made up of amateurs.