Robin van Persie scored on his return to Emirates Stadium on Sunday as Arsenal were held to a 1-1 draw against champions Manchester United, hours after both Reading and QPR were relegated from the Premier League.
In the day's other game, Chelsea resumed control of the race for Champions League qualification - beating Swansea at home to re-assert themselves in third position.
Robin van Persie scored from the penalty spot as Manchester United drew 1-1 with Arsenal on Sunday.
Van Persie cancelled out Walcott's second minute opener shortly before half-time, much to the disgust of the home support - as Arsenal only moved an additional point clear of arch-rivals Spurs in the race to qualify for next season's Champions League.
Van Persie was the centre of attention before kick-off - jokingly walking towards the home dressing room upon his arrival at the stadium, before taking the traditional guard of honour along with the rest of the United team - but his first real footballing contribution of the afternoon ironically led to an opposition goal.
The Dutchman was wayward with a difficult attacking pass, handing possession back to the Arsenal side - who quickly sprung into attack. Tomas Rosicky fed the ball through to Walcott as he sprinted clear (although there were suspicions of offside), and the forward made no mistake as he slipped the ball past David De Gea.
United tried to respond - Phil Jones missing with a great headed opening, before Wojciech Szczesny spread himself to deny Van Persie with his face - but the game was briefly more notable for a string of hasty tackles; with Van Persie, Jonny Evans and Walcott all picking up yellow cards for ill-advised challenges.
Then came a mistake from Sagna, and United's equaliser. The Frenchman gave the ball away to Van Persie deep in his own half and, in his desperation to make amends, took down the Dutchman inside the box as he threatened to shoot on goal. Van Persie coolly dusted himself down and, amid the boos from the crowd, buried his penalty beyond Szczesny. He did not celebrate the goal, his 25th of the league campaign.
The second half saw United show a bit more drive, with Arsenal also showing more organisation in defence - with the result being that both teams struggled to create clear openings. Indeed perhaps the most notable moment came when Sagna - already booked for his penalty mistake - rashly slid into Evra, but referee Phil Dowd did not produce the second yellow card it probably warranted.
As the game entered the final 20 minutes Arsene Wenger tried to change things, with Jack Wilshere, Gervinho and Alex Oxlade-Chamberlain replacing Rosicky, Lukas Podolski and Aaron Ramsey respectively.
The changes did not really have the desired effect as, while Arsenal continued to push, clear-cut chances were hard to come by. Walcott saw a rasping effort deflected over before Santi Cazorla saw his speculative effort palmed away - moments after Kieran Gibbs thought he should have had a penalty as Rio Ferdinand cleaned him out in the box.
It was all Arsenal in the final five minutes but United also had threatened - with substitute Ryan Giggs agonisingly failing to convert a quick breakaway as his shot deflected wide.
Arsenal are now two points above Spurs in fourth, with Utd now unable to surpass Chelsea's record for Premier League points.
A dispiriting, dull 0-0 draw between Reading and QPR saw both teams relegated from the Premier League on Sunday.
The goalless draw saw both sides improve to 25 points but, with three games remaining and one of Wigan or Aston Villa (who play each other on the last day of the season) guaranteed to reach at least 35 points, neither side can now mathematically clamber out of the drop zone.
In truth, on the evidence of the match at the Madejski Stadium - and, indeed, throughout the entire season - neither side deserved to stay in English football's top division. Both sides had a handful of promising chances to give themselves a stay of execution but, with both goalkeepers ultimately unbeaten, the Championship beckons next season.
Pavel Pogrebnyak and Adam Le Fondre perhaps squandered the most promising openings for the home side while QPR, who looked similarly disjointed throughout, were unable to take advantage after both Jay Bothroyd and Adel Taarabt worked themselves into dangerous positions.
For both sides the attention now turns to escaping from the Championship at the first time of asking - with QPR, weighed down by a sizeable wage bill, perhaps wondering if they will be able to offload some of their highly paid but underachieving stars.
Elsewhere, Frank Lampard moved within one goal of Bobby Tambling's club scoring record as Chelsea beat Swansea 2-0 to move back into the driving seat in the race for Champions League qualification.
Two strikes shortly before half-time - Lampard's coming from the penalty spot - saw the Blues move three points clear of Spurs in fifth, with four games left in the season. The two sides meet at Stamford Bridge on May 8.
The game itself saw the Blues gain a modicum of revenge on the Swans, who knocked the west Londoners out of the Capital One Cup at the semi-final stage earlier in the year.
It took the home side 43 minutes to break the deadlock, Brazilian Oscar beating Michel Vorm with a low drive from Lampard's pass. The England midfielder then got on the scoresheet himself, slipping his spot-kick below Vorm after Juan Mata had been fouled by Leon Britton.
Both sides created chances in the second 45 but a third goal was not forthcoming, as Chelsea successfully secured the three points they desperately need at this stage of the campaign.