Manchester City missed the chance to join neighbours United at the summit after a frustrating stalemate at West Ham.
The champions enjoyed ample possession in east London but their unbeaten start in the Premier League continues to be an underwhelming one and West Ham were denied what seemed a legitimate early goal.
Few more awkward-looking trips before Tuesday's must-win Champions League visit of Ajax could Roberto Mancini have picked out and his side would have gone behind inside five minutes had it not been for a wrongly-raised flag.
Kevin Nolan watched Mark Noble's lofted ball all the way over his right shoulder before lashing a fierce volley past Joe Hart but Sam Allardyce was left raging by the offside decision and he had a point.
Edin Dzeko was dubiously ruled offside at the other end but, in any case, missed his header on the rebound and while the hosts continued to knock the ball about with comfort, City struggled to find their groove.
Mohamed Diame cut inside and blazed goalwards, Yossi Benayoun watched a sidefoot volley hit the bar and Andy Carroll dragged a shot wide but the space Yaya Toure was allowed to stride into at the other end served as a warning.
City's best chance came from a Carlos Tevez inswinger but Mario Balotelli - wasteful on several occasions - lifted the ball over the bar from close-range and Mancini blew out his cheeks in frustration.
The Italian boss glowered in his dug-out for several minutes before his players returned but his verbal volley drew a response. City pressed higher up the pitch and a string of corners came, threatening the breakthrough.
Ex-Hammer Tevez looked like being the man, but sliced across the ball with the goal in his sight, and then Gareth Barry charged into the box only to poke past the post, that miss the cue for Sergio Aguero's introduction.
Jussi Jaaskelainen pushed away a fierce shot from the new boy, and James Collins threw his body in front of blue shirts to preserve a deserved deadlock.
Allardyce punched the air while Mancini wore a grimace: it was his side's first goalless draw since Boxing Day.