Arsenal and Chelsea both wasted the chance to boost their Champions League claims as they recorded a goalless draw in the Barclays Premier League game at the Emirates Stadium.
The third-placed Gunners hit the woodwork twice and Robin van Persie had other clear-cut chances but could not get the better of Petr Cech as the hosts edged six points clear of Tottenham having played two games more.
Otherwise, much-changed Chelsea were arguably the better side but were let down badly by their decision-making and execution in the final third as they stayed sixth in the table with just four games remaining.
The Blues felt they had an early penalty shout when Salomon Kalou got ahead of Bacary Sagna down the left. However, referee Mike Dean waved play on.
In the 13th minute, Michael Essien bundled over Alex Oxlade-Chamberlain to concede a free-kick 20 yards out on the left of centre. Walcott whipped the ball over to the far post, where Robin van Persie arrived late to stab the ball against the outside of the woodwork.
The visitors looked dangerous on the counter attack, but Florent Malouda's cross into the six-yard box was hacked clear by Laurent Koscielny.
Arsenal hit the woodwork again five minutes before the break. This time, Van Persie was the architect, his floated free-kick into the Chelsea box picking out Koscielny, whose header looped over Petr Cech, but came back off the crossbar.
Arsenal maintained the pressure, with Cech standing up well at the near post to deflect Van Persie's shot clear after another ball swept through the Chelsea box from the right by Alex Song.
Roberto Di Matteo switched Fernando Torres out to the flank for the second half, with Daniel Sturridge down the middle. Arsenal upped the tempo again, but Van Persie cracked a 25-yard free-kick high into the Clock End.
Van Persie went down in a heap under pressure from John Terry, but the referee waved away the half-hearted penalty appeals. The Dutchman then blazed wide after Terry slipped to let him into the right side of the Chelsea box.