The Red Devils got the better of the Hammers in the midweek third round replay thanks to a first half Wayne Rooney goal.
Rooney had the chance to double the lead in the second half from the penalty spot but the England international skied his attempt poorly.
United held on for the narrow win and will host Fulham at Old Trafford in the next round.
Lindegaard - 6
A clean sheet is always a confidence booster but the United goalkeeper was rarely troubled by West Ham in all honesty. His distribution was also poor.
Rafael - 6.5
West Ham didn't offer enough threat down Rafael's flank which was a big mistake as it allowed the United full-back to do what he does best which is to bomb forward with purpose.
Buttner - 7
Decent game from Buttner. His arrival has certainly given Evra a much needed kick up the backside and it is not hard to see why. The full-back was pretty solid in defence while powerful in attack.
Jones - 7
Jones gave a timely reminder to United manager Sir Alex Ferguson that he has something to offer the Red Devils as they look to win trophies on multiple fronts.
Smalling - 6.5
Didn't perform too badly but certainly was helped out by a solid game from defensive partner Jones.
Valencia - 5.5
Valencia's final ball was poor by his own high standards.
Anderson (Off 67') - 6.5
That ball in from Anderson to put Hernandez through for United's first goal, a tap-in for Rooney, was excellent.
Nani (Off 77') - 5.5
How can we sum up his latest performance succinctly? His days at Old Trafford are numbered
Giggs - 7.5
Giggs is such an intelligent footballer you can play him anywhere in midfield and he would be fine. West Ham learned a little about what that last statement means on Wednesday. He can no longer beat you for pace so he out-thinks you instead.
Rooney - 7
Played behind Hernandez but arrived at the perfect time to tap in United's only goal of the game following the Mexican's cross. Needs to work on his penalty taking, though, as it was a really lousy spot kick by the England international late in the match.
Hernandez - 7
Got caught offside way too many times but that's part and parcel of his game. He plays on the edge and it was his ability to get away from his marker and then cross which resulted in the only goal of the game.
Carrick (On 67') - 7
Came on with a job to do which was to calm things down and ensure United saw out the narrow victory.
Scholes (On 77') - 6
Scholes collected his eighth yellow card in his past 14 appearances for United against West Ham. He is starting to look a tad off the pace these days. Fantastic player he has been for United though.
Jaaskelainen - 6.5
Made some important stops during the game but was generally not that great.
Potts - 6.5
A fantastic goal line clearance from Potts only cemented his claim as one of the Premier League's rising stars.
Spence - 5.5
His positioning can be suspect at times and he needs to get rid of that nasty habit of sticking his hand out in the box.
Reid - 7
There are not too many defenders in the league who can recover lost situations as well as Reid can. He made some crucial last ditch tackles against United.
Tomkins - 6
We thought he struggled against the movement of Rooney and Hernandez.
Diarra - 6.5
A big physical presence who should be hard to get past but unfortunately for the Hammers he was not.
O'Neil - 7
Did so much hard work for West Ham in midfield against Man United. Needed to do more with possession though.
Diame (Off 65') - 6.5
When he drives against you he can be such an all-action type player. He can make things happen for West Ham but this was not one of his better days.
Taylor - 7
He will definitely want a do-over after missing a good chance in the match for West Ham to score.
Vaz Te (Off 78') - 6.5
Can be dangerous when he gets his marker on the back foot but sometimes he just lacks that cutting edge needed to truly trouble a quality team like United.
C.Cole (Off 65') - 6
Given his size and power, he should have made more out of his battles against Smalling and Jones. Doesn't turn it on enough against the big teams.
Collison (On 65') - 6
Was supposed to come on and offer West Ham an extra dimension to the team as they chased an equaliser but he never really got going.
Nolan (On 65') - 7
The one West Ham player who really had a go at exposing some of United's weaknesses. He makes intelligent runs when he doesn't have the ball and given more time on the pitch he might have pushed this tie into extra-time.
Lee (On 78') - N/A