Diego Costa made the difference as Chelsea overcame a defensive West Bromwich Albion 1-0 to return to the top of the Premier League with their ninth victory in a row on Sunday.
The Spaniard's second-half strike sent the Blues three points clear of Arsenal, who had taken the overall lead on goals scored on Saturday after seeing off Stoke City 3-1 at the Emirates.
With the game heading for a goalless stalemate at Stamford Bridge, Costa seized on a defensive error to break the deadlock with a superb shot into the top left corner in the 76th minute.
It was the league top scorer's 12th goal of the campaign, as many as he scored in all of last season.
Chelsea, who have now won nine Premier League games in a row for the fifth time in their history, have 37 points to Arsenal's 34 after 15 games.
Antonio Conte's men created very little in the first half against a stubborn side who had taken 10 points from their last four games, but the introduction of Cesc Fabregas as a 74th-minute substitute provided a breakthrough.
Fabregas played a long ball to the corner and hesitant West Brom defender Gareth McAuley, with time to clear, was dispossessed by Costa who gave goalkeeper Ben Foster no chance.
"We knew it could be difficult to create chances, they played their game, had a plan and did it very well. But thanks to this man (Costa) once again we have three points," Fabregas told BT Sport.
"Every pass I make, he makes it special. Probably it will count as an assist but it was all him today. He fought for the ball...the game was asking for a change and it happened and I'm very glad for that."
Chelsea had only one other shot on target, a long-range David Luiz free kick, although the tireless N'Golo Kante had another effort deflected wide.
West Brom, with just one shot on target, had not won at Stamford Bridge in the top flight since 1978. They are eighth with 20 points.
"It was a tough game and we prepared for this situation," said Conte. "We played with passion. West Brom is a tough team, a physical team who are difficult to break down. It was a good win and now we must continue.
"We have won nine in a row which is fantastic because this league is very tough. We are working very well."