Manchester United manager Sir Alex Ferguson says the season is approaching a crucial juncture for his side in their bid to win the Premier League.
United are top of the table, a point above champions Manchester City and seven clear of Chelsea and West Brom.
After Ferguson said: "It's a big moment for us.
"With no international football and our last [Champions League] group game next Wednesday, it gives us a further chance to concentrate on the league."
Ferguson's men took the lead at Old Trafford through Robin van Persie's deflected strike with just 32 seconds on the clock.
The fastest goal scored in the top flight this season, it was especially welcome for Manchester United given that they had conceded the opener in nine of their 13 league games before Wednesday.
Kevin Nolan and Andy Carroll had chances to equalise, while West Ham goalkeeper Jussi Jaaskelainen saved well from Javier Hernandez.
After half-time Jaaskelainen kept out Wayne Rooney and Michael Carrick before Carlton Cole and Modibo Maiga went close late on.
"We expected a tough game from West Ham - they're a very well organised, powerful team and they make it difficult for everyone," Ferguson told BBC Sport.
"We got a good start. I thought could have finished them off long before the end of the game because some of the football, in the first half particularly, was very good.
"We just couldn't get that finishing goal that would have made it easier. It's unusual for us to score early and be in front.
"Then the big plus point for us was defensively we did very well because they are a real handful.
"We're coming to a really important time in the season where our defending, if it improves, will give us a great chance. "
The last time Manchester United lost at home in the Premier League to a promoted club - Bolton in 2001 - Sam Allardyce was the manager and Nolan made it on to the scoresheet.
Neither could help the Hammers break that sequence on this occasion, although Allardyce felt his team were unfortunate.
"I'm not so sure, in the end, if Manchester United created another chance to score," said the 58-year-old.
"It was a resilient performance and we had a couple of chances at the end. It was a great effort but unfortunately another defeat.
"I'm encouraged by fact we limited United at Old Trafford to little or no chances. I feel a bit sorry for the lads because of the way we lost."
West Ham were beaten at Tottenham on Saturday and they face a daunting run of fixtures against Chelsea, Liverpool, West Brom, Everton, Arsenal and Reading in December.
"We were stretched, we've been stretched for a while. Noble was suspended, four or five are injured," Allardyce added.
"We could do with players getting fit. We play three games in less than six days so we need a really good recovery before Chelsea.
"We have to perform like we did today, with a bit more on the front line."