Already the first boss of the Roman Abramovich era not to oversee a victory in his opening two games under the Russian, it got worse for Rafa Benitez at Upton Park.
Mata appeared to ease the pressure on the former
Liverpool boss by ending the European champions' five-hour, 34-minute goal drought after 13 minutes yesterday.
But the visitors squandered several chances to score again and were deservedly made to pay through a controversial Carlton
Cole leveller and goals from substitutes
Mohamed Diame and Modibo Maiga.
Fernando Torres led
Chelsea's attack and he burst in behind onto
Victor Moses' 13th-minute through ball and coolly cut it back for Mata to sidefoot home easily.
Mata could have made it 2-0 in the 40th minute when he fired Moses's cutback too close to
Jussi Jaaskelainen and saw his follow-up blocked.
Sam Allardyce had seen enough by the break, sending on Matt
James Tomkins and
Both had the desired effect and in the 63rd minute Matt Jarvis' cross looped up off
Cesar Azpilicueta and
Carlton Cole climbed all over Ivanovic to nod it in.
Although Chelsea enjoyed some pressure,
West Ham were not to be denied. With four minutes left, a throw-in found Cole who laid the ball off to Diame to drill home. It got worse in stoppage-time when fellow sub Maiga followed up after Taylor's shot was saved.