Arsenal moved on to 67 points with seven matches to play to lead the standings for the first time since January and keep the pressure on Manchester United and Chelsea, who play their weekend matches on Sunday.
United, who host Liverpool at Old Trafford, have 66 points from 30 games, followed by Chelsea who have 64 points from 29 and visit Blackburn Rovers.
Tottenham Hotspur maintained their push for fourth place and a possible Champions League berth when they won their fourth successive league match with a 2-1 success at Stoke City and moved on to 55 points from 30 games.
They are followed by Liverpool (51 points), Manchester City (50) and Aston Villa (50), who were held to a 2-2 draw by Wolverhampton Wanderers in Saturday's early kick-off.
FIRST DISMISSAL
Arsenal, who last lost in the league to Chelsea on February 7, went ahead through Brazilian Denilson after only five minutes.
They sealed the victory when Cesc Fabregas, returning from injury, scored with an 82nd minute penalty for his 15th league goal of the season after Matthew Upson handled.
However, the hosts had to play the whole of the second half with 10 men following the 44th minute dismissal of centre-back Thomas Vermaelen who became the first Arsenal player to be sent off this season.
But the decision was a harsh one after West Ham's Mexico striker Guillermo Franco went down somewhat easily under the Belgian international's challenge in the box.
Alessandro Diamanti then saw Manuel Almunia save his penalty, although the goalkeeper escaped censure from officials after clearly moving off his line before the kick was taken.
The defeat, West Ham's fourth straight league loss, left them in 17th place just three points above the relegation zone.
Fabregas told ESPN it was unfortunate Vermaelen would now be banned but added: "We don't want to make any excuses, we want to go all the way to the title and prove we can do it".
West Ham manager Gianfranco Zola said: "In the first half we played the best we've played all season and certainly deserved something more but in the second half, although we had the extra man we lost a bit of discipline.
"I'm disappointed because it was a big opportunity for us."
SPURS ADVANCE
Earlier, Arsenal's north London rivals Spurs edged closer to a possible Champions League place after their victory at Stoke.
Goals from substitute Eidur Gudjohnsen and Niko Kranjcar earned the win against a home side reduced to 10 men early in the second half when Dean Whitehead was dismissed.
Gudjohnsen replaced injured Russia striker Roman Pavlyuchenko after 36 minutes and scored his first goal for Tottenham 10 minutes later when he lashed the ball into the roof of the net.
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