London: Diego Costa marked his return to Chelsea duty by scoring the opening goal in a 2-0 victory over Hull on Sunday that saw the Premier League leaders go eight points clear after Arsenal went second by coming through late penalty drama.
Brazil-born Spain forward Costa, who took his Chelsea tally for the season to 15 league goals, missed last weekend's 3-0 win at champions Leicester City due to an apparent back complaint.
But Costa, the Blues' leading scorer, was reported to have had a training-ground row with fitness coach Julio Tous, amid speculation he had been the subject of a mega-money offer from Chinese club Tianjin Quanjian.
Following a sickening clash of heads between Chelsea's Gary Cahill and Ryan Mason that saw the Hull man taken to hospital, Costa struck in the seventh minute of first-half stoppage time when he turned in a Victor Moses cross.
Hull, belying their position of second bottom in the table, pushed Chelsea hard and might have had a penalty before Cahill sealed victory for the hosts nine minutes from time at Stamford Bridge when he ran on unchallenged to head in Cesc Fabregas's free-kick.
Chelsea manager Antonio Conte praised Costa's display, telling Sky Sports: "His performance was good and I am pleased for this.
"In the press conference before the game a lot of people asked me about his form, his attitude, and I said I took the best decision for the team, and I think I made the best decision after this performance."
Hull boss Marco Silva added: "It was not what we wanted from the game. We came here to compete, to take points."
Earlier in London, 10-man Arsenal beat Burnley 2-1 at the Emirates Stadium in a match where both sides scored penalties in stoppage time.
Shkodran Mustafi's first Arsenal goal put the home side 1-0 up in the 59th minute.
That was still the score when, in the third of seven minutes of time added on, Burnley's Ashley Barnes was fouled inside the area by Francis Coquelin and referee Jon Moss awarded a penalty.
Andre Gray, a childhood Arsenal fan, scored from the ensuing spot-kick but there was more drama to come.
With virtually the last attack of the game, Arsenal's Laurent Koscielny was caught by Ben Mee's high foot as he attempted to head in and Moss once more pointed to the spot.
Alexis Sanchez, showing remarkable nerve, chipped a penalty down the middle to give the Gunners three valuable points.
By that stage Arsenal manager Arsene Wenger had been sent off after his furious reaction to Burnley's penalty.
Arsenal had to play the final 25 minutes down to 10 men after midfielder Granit Xhaka was shown a straight red card for a reckless challenge on Steven Defour.
"We finally got the win but of course it was very difficult for us," Wenger told the BBC. "Every week and every game is an unbelievable fight for everybody."
Burnley manager Sean Dyche insisted Arsenal's decisive penalty ought not to have been awarded because Koscielny was offside.
"We know how tough this division is but you need officials to make the right decisions and that is the shame today," he said.
Victory saw Arsenal leapfrog both Liverpool, beaten 3-2 by Swansea on Saturday, and Tottenham Hotspur, held to a 2-2 draw by Manchester City, in the table.
Southampton marked their first match since former captain Jose Fonte's ?8 million ($9.9 million, 9.2 million euros) move to West Ham on Friday by ending a run of four straight league defeats with a 3-0 win at home to struggling Leicester.
Goals from James Ward-Prowse and Jay Rodriguez gave the Saints a 2-0 interval lead before Dusan Tadic's penalty four minutes from time rounded off a comfortable win at St Mary's.
Leicester's 11th defeat of the season left them just five points above the relegation zone.
Foxes manager Claudio Ranieri blamed himself for the latest loss and promised to revert to the formation that proved so successful during their shock title triumph last season.
"The players are used to 4-4-1-1 and know the positions, but I made a mistake," he said.
"I think it is much better to give them what they know well."
