Chelsea missed the opportunity to go eight points clear at the top of the Barclays Premier League by drawing 1-1 against Southampton in an entertaining game at Stamford Bridge where the officials' decisions will once again be scrutinised.
Jose Mourinho's men were looking to respond from their European exit by tightening their grip on the title after Manchester City's loss at Burnley and went in front through Diego Costa's first Premier League goal in almost two months.
Dusan Tadic equalised after a contentious penalty, awarded for a foul by Nemanja Matic on the impressive Sadio Mane.
Replays showed Matic slid in from behind and made contact with the ball, but referee Mike Dean pointed to the spot and booked the Chelsea midfielder.
Chelsea might have had a spot kick of their own for a Tadic foul on Branislav Ivanovic, but then Dean gave the Blues the benefit of the doubt rather than reduce them to 10 men for all but the opening minute of the second half.
Matic could have marked his domestic return following a two-match ban for his dismissal against Burnley with another sending off, but he avoided a second booking for a foul on Mane within seconds of the restart.
Chelsea, under pressure for much of the contest, finished on the attack, but Fraser Forster made fine saves from Oscar, Eden Hazard and Juan Cuadrado to earn Saints a point.
The Blues, who are six points clear at the top, still have a game in hand on City and remain firmly in control of their bid for a first Premier League title in five years.
Wednesday's away goals loss to Paris St Germain, which saw Chelsea tumble out of the Champions League at the last-16 stage, saw the Blues subjected to plenty of scrutiny and Mourinho launch a robust defence.
With the Capital One Cup already secured, Mourinho vowed the Blues would add the Premier League to complete a "fantastic season".
Nine wins in the remaining 11 games was Mourinho's target, prior to City's defeat at Turf Moor, and Chelsea began well against a Saints side with two wins in their previous seven.
The hosts went in front as Costa netted his 18th Premier League strike of the season and first since the January 17 win at Swansea after 11 minutes.
Hazard played the ball wide for Ivanovic to cross and an unmarked Costa headed in from six yards.
Thibaut Courtois had to save from Mane after a move involving former Chelsea ma Ryan Bertrand and Tadic before Saints equalised from the spot when Matic was adjudged to have fouled Mane after his one-two with Victor Wanyama.
Matic was booked and there were few complaints from Chelsea's players before Tadic's penalty went in and Chelsea assistant boss Rui Faria was sent down the tunnel to watch the replay.
Ivanovic was then tripped by Tadic in the right side of the area, but the right-back's theatrical fall dissuaded Dean from awarding what would have been a just penalty.
It evoked memories of the December 28 draw at St Mary's when Cesc Fabregas was booked for diving and Mourinho afterwards spoke of a "clear campaign" against Chelsea.
Mourinho was fined £25,000 for those comments and would have been relieved Chelsea got the benefit of the doubt early in the second period when Mane wrong-footed Matic and was tripped.
The Serbia midfielder was fortunate not to receive a second Premier League red card in successive appearances and soon he was replaced by Ramires.
It was a sign of the pressure Southampton exerted on Chelsea, whose often commanding centre-backs John Terry and Gary Cahill were troubled by the pace of Mane and Shane Long.
Courtois saved from Tadic and Mane late in the first half, but Chelsea struggled to create similar chances to test Forster.
Morgan Schneiderlin barged Fabregas over before Costa flicked Willian's volley on to a post and then acrobatically hit Hazard's cross back to the Belgian, who headed in from an offside position.
Jose Fonte, who was pushed by Costa after an earlier exchange, made a well-timed tackle to deny the striker.
Cahill blocked a Long effort before Ivanovic was booked for bringing down Mane and Wanyama was also cautioned for a foul on Hazard.
Mane then bamboozled Cahill, who was booked, as his searing pace continued to trouble Chelsea, who then hemmed Saints deep in their own half.
Forster made a double save to keep out Oscar's header and Hazard's follow-up and then saved from Oscar again.
Costa blasted over under pressure before Forster saved from Cesar Azpilicueta.
From the resulting corner he denied substitute Juan Cuadrado, while Terry had a follow-up effort blocked on the line and then lashed wide as Saints held on.