Arsenal twice hit the woodwork as Barclays Premier League title rivals Manchester City somehow left Emirates Stadium with a goalless draw.
Robin van Persie and Cesc Fabregas both saw their first-half shots come back of the base of the same post.
City then had keeper Joe Hart to thank after he produced a wonderful fingertip save to deny Van Persie on the hour as Arsenal had to be content with only a point. Both teams finished with 10 men after full-backs Pablo Zabaleta and Bacary Sagna were shown straight red cards by referee Mike Jones for a needless clash on the far touchline.
Van Persie was the first man to hit the City goalframe, after nine minutes, when he created space for a shot and drilled the ball against the base of Hart's right-hand post.
After 27 minutes, Arsenal again hit the woodwork. Nasri and Fabregas broke down the left, with the Arsenal skipper cutting back inside to wrongfoot Hart only for his shot to bounce off the post.
From the rebound, Walcott smashed an angled drive against the other upright, but the offside flag was already raised.
There was a warning for Arsenal when City broke quickly down the right and Carlos Tevez drilled the ball just over from 20 yards.
On the hour, Hart made a fantastic save to send a goal-bound 25-yard drive from Van Persie over the crossbar.
Both teams finished the match with 10 men after full-backs Zabaleta and Sagna were shown straight red cards after pushing their heads together.
City held on for a point which keeps them second but sees leaders as Manchester United the night's big winners.