Wayne Rooney scored his first goal in open play since March as leaders Manchester United won away in the Premier League for only the second time this season with a 2-1 victory against West Brom.
The result of Saturday's early kick-off match left United three points clear at the top ahead of Manchester City.
But City can get back level on points with their local rivals if they beat Blackpool at Eastlands later on Saturday.
Rooney opened the scoring but it was substitute Javier Hernandez, who netted both goals in United's other away league win this term, a 2-1 success at Stoke in October, who sealed victory 15 minutes from time at the Hawthorns after the Baggies' Peter Odemwingie had missed a penalty.
England striker Rooney put United 1-0 up as early as the third minute at the Hawthorns when he stooped to head in a Patrice Evra cross.
But West Brom were level 11 minutes later when James Morrison lashed the ball in from 25 yards out.
The hosts had a penalty just after the hour when United's Rio Ferdinand brought down Jerome Thomas in the box.
But although Odemwingie sent Tomasz Kuszczak the wrong way, he scuffed his shot so badly that the ball went well wide of the keeper's right post.
And United punished that miss when unmarked substitute Hernandez headed in from a corner.