Two early goals in two minutes from Ole Gunnar Solskjaer and Juan Sebastian Veron with a spectacular 25-metre free kick ensured United's fourth consecutive league win well before defender Sebastien Schemmel's 61st minute own goal.
United are now level on 35 points with champions Arsenal, who face Tottenham Hotspur in Sunday's north London derby, and are one point ahead of Chelsea.
United, whose title bid is very much under way after wins over Arsenal and Liverpool, dominated throughout at Old Trafford and also welcomed back David Beckham to league duty as a second half substitute after a month's injury absence.
"A 3-0 scoreline's very good -- I'm pleased with that," United manager Alex Ferguson told SkySports. "We had to work for it....and we played some fantastic football at times.
"Veron's goal was fantastic, we got a break with the third goal -- the kind of break we weren't getting a few weeks ago. It's the kind of break West Ham are needing."
Asked if his team could stay at the top, Ferguson said: "At the end of December, beginning of January, we'll have a good idea how the league is shaping up.
"We want to be there, the players have shown the determination to be there and I think we've got a good chance."
West Ham manager Glenn Roeder, whose side stay rooted to the bottom of the table, said: "We've come up against a Manchester United side in full flow and it tells you what you're up against when England's captain David Beckham is sitting on the bench."
CHELSEA DRAW
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Ranieri played down the setback, saying: "In front of us there was a big team in Middlesbrough -- they played very, very well.
"In the first half, we created two or three good chances to score and they scored first. That's football.
"The second half was more tactical, but both teams wanted to win. In every action, players showed a real will and that's important for us. It was an interesting match between two good squads playing good football."
Teenage sensation Wayne Rooney got Everton back to winning ways after two consecutive defeats -- making one and scoring another in their 2-1 comeback win against Blackburn Rovers.
The home win moved Everton up to fourth in the table, one point ahead of arch rivals Liverpool, who play at Sunderland on Sunday and who face Everton in next weekend's Merseyside derby.
Everton manager David Moyes said: "We went behind, but all credit to the lads, we got a goal back quickly which helped and to get the second one put us in the driving seat."
As for Everton's remarkable season, Moyes said: "We're fourth in the table and that's a wonderful position to be in.
"I don't know of anyone who wouldn't have settled for this position at the start of the season. But I think we should be even higher." Thomas Hitzlsperger's stoppage-time shot earned 10-man Aston Villa a 2-1 home win over West Bromwich Albion in the Midlands derby, Southampton held Newcastle United 1-1 at St Mary's and Charlton Athletic drew 2-2 with Manchester City at The Valley after squandering a 2-0 second-half lead.
