Chelsea reclaim top spot while United see off Tottenham
Chelsea regained a three-point lead in the Premier League title race after Diego Costa's 12th goal of the season broke West Brom's stubborn resistance at Stamford Bridge.
Antonio Conte's side made it nine wins on the bounce with the 1-0 victory but needed until the 76th minute to see off the Baggies.
Costa, the division's top scorer, produced a worthy winner, robbing Gareth McAuley before blasting home in style.
Manchester United ended a frustrating run of four consecutive home draws in the league with an impressive 1-0 win over Tottenham at Old Trafford.
Henrikh Mkhitaryan, who has had to wait patiently for his opportunity under Jose Mourinho, grabbed the only goal after 29 minutes.
The Armenia international, who opened his account for the club in the Europa League on Thursday, ran on to Ander Herrera's pass and lashed emphatically beyond Hugo Lloris.
Mkhitaryan left the field on a stretcher after suffering an ankle injury late on but the post-match prognosis suggested he had avoided a serious injury.
At Anfield, Liverpool dropped two points to West Ham but it might have been worse were it not for a Darren Randolph gaffe.
Adam Lallana put the third-placed Reds ahead after only five minutes but the Hammers, badly in need of points to stay clear of the bottom three, were 2-1 up at the interval.
Dimitri Payet and Michail Antonio scored in the 27th and 39th minutes but when Randolph dropped a cross at Divock Origi's feet just after the restart, hopes of an away win vanished.
Southampton's record signing Sofiane Boufal also scored for the first time in the Premier League as Saints edged past Middlesbrough 1-0 at St Mary's.
The £21million man fired home from 25 yards eight minutes into the second half, lifting Southampton into the top half of the table.