Costa scored during nine minutes of added time at the end of the first half, side-footing home from Victor Moses' cross for his 52nd Chelsea goal in his 100th appearance.

An injury to Hull midfielder Ryan Mason, who clashed heads with Gary Cahill early in the game, was the reason for the long spell of stoppage time.

Mason was given a standing ovation as he departed on a stretcher after receiving treatment but Cahill was able to continue and, with 10 minutes remaining, sealed the points when he headed home a Cesc Fabregas cross.

Alexis Sanchez scored a last-gasp penalty as 10-man Arsenal beat Burnley 2-1 to go second in the Premier League.

It looked as though the Clarets would take only their second point away from home this season when Andre Gray powered home a stoppage-time spot-kick to cancel out Shkodran Mustafi's first Arsenal goal.

But in the last of seven additional minutes, referee Jon Moss -- who had already dismissed Granit Xhaka and sent Arsene Wenger to the stands -- pointed to the spot once again and Sanchez sealed a remarkable 2-1 win.

Mustafi had put Arsenal in front soon after the break with his first goal for the club, but Xhaka's ninth red card since 2014 left the Gunners a man down.

Struggling Premier League champions Leicester City suffered another away day to forget as they lost 3-0 at Southampton.

The home side had the better of the contest from the start and broke through after 26 minutes when Cedric Soares teed up James Ward-Prowse, who bent home a fine finish.

A little over 10 minutes later it was 2-0 as Ward-Prowse created havoc with a whipped free kick into the area and the ball broke off defender Wes Morgan for Rodriguez to thump it home from close range, and Dusan Tadic added a third from the spot after Shane Long had been brought down by Morgan.