Two goals in five minutes from Reading's escapologist-in-chief, Adam Le Fondre, earned the Royals a point and left Chelsea stunned. For the preceding 87 minutes, a fifth successive away league win had seemed a formality.
But Le Fondre, who scored two in six minutes in Reading's last game to defeat Newcastle, had other ideas. The substitute ensured a nervy climax with an 87th-minute left-foot strike and then stunned Chelsea with an equaliser in added-time.
Benitez had pointed to fatigue before this game but made minimal changes from the 2-2 FA Cup draw with Brentford in pursuit of a win that was non-negotiable for his employers. The invaluable Mata replaced Marko Marin and Cesar Azpilicueta returned in place of John Terry. Reading had six changes from the side that dispatched Sheffield United 4-0 at the weekend.
Not content with plundering four goals against the Blades, Reading also recruited Nick Blackman, who had scored 14 goals for the League One club this season but signed too late to make the squad here.
The home side had made a habit of stirring comebacks recently, winning from behind against West Brom and Newcastle in their last two league games.
However, they began as if the intention was to avoid having to mount a similar operation against Chelsea, with five men strung across midfield and Pogrebnyak working hard to cut off supply from the visitors' back four as his team-mates dropped off and waited.
It made for a game as congested as the M4 outside, with the give and take between supporters the most diverting element of the opening exchanges.
Chelsea fans once again took the opportunity to revel in the mindless abuse of Benitez. It is appalling, self-defeating stuff, but as they never fail to remind us, they are Chelsea and they know who they are. Make no mistake, they know it is counterproductive, that it undermines the coach and inhibits their team. When the Reading supporters sang "Rafa Benitez, he thinks you're all scum" the Chelsea contingent stood and applauded.
There was little to rouse a similar response on the field until Mata underlined his importance to Benitez and Chelsea with a goal in first-half stoppage time that was unworthy of the 45 minutes that preceded it.
Ramires and Oscar combined to find the Spaniard on the edge of the Reading box with his back to goal. He laid the ball off to Fernando Torres and set off for the six-yard box, where Torres' neat chipped pass found his run. The first-touch left-foot finish past Adam Federici was a formality.
With Plan A exposed Reading had no choice but to be more positive after half-time – they could hardly have been more negative before the break – but it left them exposed to Chelsea's counter-attacks. They escaped narrowly once when Ian Harte denied Torres as the Spaniard shaped to meet Oscar's cross three yards, but respite proved brief.
From the resulting corner Lampard rose high above Hart to thump a header into the top left-hand corner, the ball evading Pogrebnyak's attempted clearance on the way in. The goal prompted a round of "Sign him up!" from the fans who remain devoted, even if Roman Abramovich is not. (© Daily Telegraph, London)