Mourinho's teams were never beaten on their home patch in the top flight during his first spell in charge, and they have embarked on another undefeated run since the Portuguese returned to the club in the summer.
They were in peril at 2-1 behind against the Baggies deep into stoppage time, however referee Lee Probert deemed Steven Reid to have fouled Ramires in the penalty area and handed Chelsea a spot-kick.
Eden Hazard, in Mourinho's bad books earlier in the week after a passport blunder, converted with a cheeky pass into the bottom right corner.
It meant Mourinho's former assistant Steve Clarke was denied a famous win over his old boss, whose team nevertheless slipped to fourth place in the table, behind Southampton and Liverpool, plus leaders Arsenal.
Chelsea went ahead with a close-range poacher's finish from Samuel Eto'o right on 45 minutes, but Shane Long gave a warning of what was to come when he headed against the left post early in the second half.
Long equalised in the 60th minute, nodding in from close range after Petr Cech powered a thumping header from Gareth McAuley, and Stephane Sessegnon then fired the Baggies ahead eight minutes later when his low left-footed shot embarrassed the Chelsea goalkeeper.
West Brom protested long and hard about the late penalty, which looked soft, but Hazard took full advantage.
Beaten by Arsenal in their last outing when top spot was up for grabs, Brendan Rodgers' side responded positively and Luis Suarez scored twice against Martin Jol's side.
Their breakthrough goal came from an opponent in the 23rd minute, as Fernando Amorebieta headed the ball into his own net under pressure from men in red shirts after Steven Gerrard whipped over a free-kick.
Defender Martin Skrtel scored the second three minutes later, meeting a corner from the right delivered by Gerrard and heading in at the near post.
Almost inevitably, striker Luis Suarez got in on the scoring action with Liverpool's third in the 36th minute, firing past Maarten Stekelenburg after good work from Jordan Henderson. And the Uruguayan cracked in the fourth too, after 54 minutes, with Gerrard setting up his third goal of the game.
Liverpool closed to two points behind leaders Arsenal, whose next assignment comes at Manchester United on Sunday.
Morgan Schneiderlin headed the home side in front after 16 minutes, Ricky Lambert's penalty on the half-hour mark doubled Southampton's lead, and a fine solo goal from Adam Lallana - called up by England this week - capped a fine 45 minutes from Mauricio Pocchetino's men.
Yannick Sagbo pulled one back for Hull early in the second half but an 88th-minute effort from Steven Davis restored the three-goal cushion.
With 15 minutes remaining their Villa Park tussle was goalless, but Leandro Bacuna's free-kick and Libor Kozak's header in the close quarter of an hour gave Villa the points.
West Ham boss Sam Allardyce had labelled the match a "six-pointer" earlier in the week and it was his side who dominated the first half and duly led at the break courtesy of Ravel Morrison's third league goal of the season.
The Canaries were jeered off at half-time but emerged a much more cohesive unit as Gary Hooper scored his first league goal for the club from the penalty spot before Robert Snodgrass curled in a match-winning free-kick and Leroy Fer added a late effort to secure a 3-1 win.