Didier Drogba's free-kick shortly before half-time cancelled out Hull's opener scored by Steven Mouyokolo but Chelsea could not force the winner after the break despite late pressure.
Carlo Ancelotti's Chelsea have 55 points from 24 games with champions United on 53. Third-placed Arsenal, who play at Chelsea at the weekend, are on 49 points.
Hull, one of four sides on 21 points near the foot of the table, remain in the relegation zone on goal difference.
While Chelsea's form at Stamford Bridge has been immaculate with just two league points dropped all season, they have been far less impressive away from home and they were not at their best again on Tuesday.
Chelsea began well with Frank Lamaprd and Michael Ballack both forcing Hull keeper Boaz Myhill into early action but they lost their way as the first half wore on and fell behind to the kind of set piece that has troubled them all season.
Stephen Hunt swung in a corner and Mouyokolo found himself unmarked to head past Petr Cech from close range.
The goal stung Chelsea into action and Hull's joy was cut short three minutes before halftime when Drogba curled in a free kick for his first goal since returning from African Nations Cup duty with Ivory Coast.
Anthony Gardner missed a great chance to put Hull back into the lead while Daniel Sturridge nearly grabbed a vital win for Chelsea with a late effort saved by Myhill.
Chelsea skipper John Terry, who is mired in controversy after newspaper allegations about his private life, had a quiet night although he was subject to abuse by Hull fans.
Terry's future as England captain could be decided this week by coach Fabio Capello.
