A Samuel Eto’o hat-trick means Chelsea are on course for an emphatic victory at Stamford Bridge despite being on the back foot for much of the first half.
The striker, selected ahead of Fernando Torres, opened the scoring with a deflected effort on 16 minutes and his close-range finishes either side of half-time appear to have sealed Manchester United’s fate.
Chelsea went ahead when Eto’o went past Phil Jones and his shot from near the edge of the penalty area looped over keeper David de Gea via the boot of the unfortunate Michael Carrick.
United had made a lively start, with Petr Cech blocking Ashley Young’s low shot after the wide-man had exchanged passes with Danny Welbeck.
And David Moyes’ side also threatened after going behind, Patrice Evra firing into the side netting before Cech was called upon to make another save.
An off-balance Gary Cahill failed to cut out Adnan Januzaj’s low cross but Welbeck, who felt he was impeded by Cesar Azipilcueta, was unable to direct his shot past the Chelsea keeper.
Eto’o, on the other hand, made no mistake when found by Cahill’s low cross after a corner was only half-cleared in first-half injury time.
The same players were involved in Chelsea’s third three minutes after the break, Eto’o following up to score after De Gea had kept out Cahill’s header from Willian’s right-wing corner.
Chelsea (4-2-3-1): Cech; Ivanovic, Cahill, Terry, Azpilicueta; Ramires, Luiz; Willian, Oscar, Hazard; Eto’o.
Subs: Schwarzer, Cole, Mikel, Matic, Lampard, Mata, Torres.