Raul Meireles drilled the game's first effort of note into De Gea's side-netting after United had failed to clear a corner, but the visitors were soon up in arms when Danny Welbeck was sent tumbling by Gary Cahill on the edge of the Chelsea area, only for referee Howard Webb to wave away the appeals.
Frustration and carelessness reigned for both sides in the opening half-hour, as possession was traded and promising openings were squandered with abandon. The Reds' clearest sight of goal came as Michael Carrick released Rooney down the right, but Branislav Ivanovic slid in to nick the ball to safety before Welbeck could tap in a simple conversion.
Fittingly, the game's opening goal was far from easy on the eye. Daniel Sturridge was allowed to pick his way to the byline on the Chelsea right, deep inside the United area. As the ex-Manchester City striker jabbed a cross into a crowded six yard box from point-blank range, De Gea flicked out a boot, but only diverted the ball against the helpless Evans, off whom it ricocheted into the unguarded goal.
As Stamford Bridge's home support revelled in a surprise lead, Sturridge immediately drew a full-length save from De Gea with a stinging drive. The remainder of the half, however, belonged to United. A curling effort from Young, a snapshot from Welbeck and a long-range rasper from Rooney all forced Cech into scurrying saves, but the absence of tangible reward for greater promise characterised the Reds' first half.
Hopes of a comeback were seemingly dashed, however, within five minutes of the restart. Chelsea's first foray forward culminated in Fernando Torres being given time to pick out a target from the right, and his deep cross fell perfectly for Mata to lash a brilliant volley into the roof of De Gea's net from six yards.