Michael Owen scored for the first time since that hat-trick at Wolfsburg in December as the Red Devils closed to within a point of Premier League leaders Chelsea.
But Owen's late effort was a mere footnote compared to Rooney's contribution, which took his tally for the season to 27.
The 24-year-old has been set a conservative target of 30 by Sir Alex Ferguson. At this rate he will eclipse the 42 that helped turn Cristiano Ronaldo into the world's best player two years ago.
"My biggest concern was how we were going to maintain the scoring level," reflected Ferguson in his programme notes as he considered Ronaldo's summer exit for Real Madrid. "There you have the answer," he added. Not that anyone needed it.
Rooney has a maximum of 17 games to overhaul Ronaldo's 2007-08 tally. On present form it is well within range.
A week ago, United were engaged in that amazing Champions League encounter with AC Milan in the San Siro, which could have been disastrous but turned out to be one of the great European results.
Rooney grabbed all the headlines, just as he has been doing for most of the season as he has dragged United along in pursuit of glory.
Where the Red Devils would be without the striker does not bear thinking about. Little wonder Ferguson once again opted to stick with him against supposedly lesser opposition on home soil when probably, he could do with a rest, however minimal.
The wisdom of the selection was proved just before half-time when Rooney planted his diving header into the corner of Robert Green's goal.
Prior to that, Darron Gibson had been the hosts' main threat, repeatedly taking aim from distance, without really threatening to beat Green's blockade.
It would be churlish to exclude Dimitar Berbatov and Antonio Valencia from praise given the Bulgarian's excellent crossfield pass and an even better volleyed cross to the far post from the South American.
But Rooney was the man who had shifted into space, Rooney who had to finish. There was never any prospect of him failing.
Unlike Milan, West Ham did not reach half-time unable to believe they were not ahead.
Gianfranco Zola might have pondered how fortunate Ben Foster had been, though.
Handed his first start since November, but surely too late to earn a call-up for England's friendly against Egypt next week, Foster was in direct opposition to another member of Fabio Capello's expanded squad.
But he would have been hanging his head in shame if he had pushed a Guillermo Franco shot that looped skywards off Gary Neville into his own net rather than directly onto his line.
The loss of Anderson to a knee injury sustained when no one was near him does not auger well for a positive conclusion to the Brazilian's disappointing season.
It was Rio Ferdinand's absence that really got tongues wagging though as United officials were unable to shed any light on his non-appearance, which could cost him the England captaincy he was due to inherit from John Terry against Egypt if injury is confirmed.
Injury is the one thing Capello cannot countenance for Rooney. There would be no point in the Italian trying to put on a brave face. England would instantly be reduced from contenders to also-rans.
In a very similar manner to his opener, Rooney found himself in splendid isolation when Berbatov released Valencia with another excellent pass in the build up to the second.
Once again the cross was inviting. Once again Rooney sent it past Green.
For a player of his class, his finishes had been routine.
Less so was the strength required to bundle Green off the ball and the eye for an opportunity as Rooney fired goalwards from the touchline.
Had Julien Faubert not been stood on the line, it would have been an incredible finish to a hat-trick.
Instead, Owen grabbed the third after an inspired through ball from Paul Scholes.
It was Owen's eighth of the season, only one short of Berbatov's tally. A long way behind Rooney though.