Chelsea mounted an inevitable response with Luiz's swerving free-kick booted away by David De Gea and Eden Hazard pulling a shot wide following an outstanding jinking run. With Rio Ferdinand making some important clearances, despite being booed by the home crowd, United seemed in control until Roberto Di Matteo's team upped the pressure as the break approached.
Evans deflected a John Obi Mikel cross against the outside of his own post from a quick throw-in and the tireless Rooney diverted Gary Cahill's header off target from the resulting corner. It became one-way traffic and only a brilliant diving stop by De Gea kept out Torres' header from a Mata cross.
It became merely a question of whether the Reds could hold on until the half-time whistle and Rooney's rash trip on Hazard, earning a rare yellow card for the England international, presented Mata with an ideal opportunity in the centre of the goal, just outside the box. The Spaniard, thwarted by a De Gea wonder-save in the closing stages of last term's 3-3 draw, this time got the better of his compatriot with a perfectly-placed free-kick.
A poor kick-out by De Gea allowed Mata to scamper onto a Torres pass but the keeper atoned with a fine block as United went into the interval with a slender lead. Despite starting the second period with more attacking threat, Luiz handling a Valencia centre from close range inside the box, Sir Alex's side conceded an equaliser eight minutes into the half.
Mata showed great control after Evans felt he would not reach a long ball and, although his cross brushed off Ferdinand's head after the No 10 was forced wide, Oscar recycled it into the box for Ramires to outjump Tom Cleverley and head in for 2-2. With Chelsea's tails up, only De Gea's near-post save denied Hazard after he skipped past Rooney and the Belgian was then unable convert a superb pass by Mata.