United down to bare bones at back
Patrice Evra was the only first-choice defender on show for Alex Ferguson's men with Rio Ferdinand, Nemanja Vidic, John O'Shea, Jonny Evans and the Da Silva brothers, Rafael and Fabio, all missing for the Premier League match.
In an unfamiliar starting lineup, Tomasz Kuszczak continued to deputise in goal for Edwin van der Sar while midfielder Darren Fletcher went to right back alongside centre halves Gary Neville and Wes Brown, with Frenchman Evra on the left.
"It's a big day for us because we had six defenders missing before the game and, of course, Gary Neville then goes off after 30 minutes and it put us under pressure," Ferguson told Sky Sports.
United lost captain Neville in the first half to a groin problem forcing substitute midfielder Michael Carrick to come on at centre back in an unrecognisable back four.
The injury absence of West Ham top scorer Carlton Cole could not have been more welcome for Ferguson as Brown then became a second-half casualty meaning United finished the match with a back four of Fletcher, Carrick, Evra and winger Ryan Giggs.
"We are down to the bare bones I am afraid," the Scot said.
Despite their problems second-placed United stayed hot on the heels of leaders Chelsea with superb strikes from midfielders Paul Scholes and Darron Gibson and two more from Antonio Valencia and Wayne Rooney.
"He (Gibson) is capable of scoring from outside the box, he has fantastic power and, again today, a wonderful hit," added Ferguson after Gibson's long-range double beat Spurs in the League Cup quarter-final in midweek.
"We finished it well. Once we got that second goal we never stopped, we went to try and kill the game off."
United visit German side VfL Wolfsburg in the Champions League on Tuesday having already qualified but need to clear their treatment room to keep themselves in the title hunt.
"I'm hoping that Vidic will be okay for Tuesday... we will probably play Michael Carrick (at centre back) again, I thought he did very well," Ferguson added.
Following the Champions League clash United have three league matches in a week beginning at home to Aston Villa on December 12 before hosting Wolverhampton Wanderers three days later and travelling to Fulham on December 19.