Salomon Kalou salvaged a point and preserved Chelsea's 85-match unbeaten home record at the end of a breathless encounter with Manchester United.
The visitors had led for much of the contest following Park Ji-Sung's first-half tap-in.
But 10 minutes from time, after Nicolas Anelka, Didier Drogba, Joe Cole and Michael Ballack had tried and failed to break down United's stubborn defence, Kalou exposed United's poor offside trap by nodding home John Obi Mikel's free-kick 10 minutes from time.
Sir Alex Ferguson's decision to play Park and Darren Fletcher worked a dream, especially with the Scot switching to the middle of midfield, a move that saw Owen Hargreaves take up a right-wing station.
Identifying Chelsea's full-backs Jose Bosingwa and Ashley Cole as major attacking threats, Ferguson chose to put his two most energetic men in direct opposition, keeping the home pair occupied defensively and stifling their threat in attack.
Despite their poor recent form, the Red Devils showed their attacking intent from the start, when Fletcher turned Hargreaves' low cross wide, and Chelsea, having lost Deco just before kick-off after the Portugal star was injured in the warm-up, could not get into their stride even though they could call upon Michael Ballack as replacement.
Luiz Felipe Scolari's team was further disrupted when Ricardo Carvalho hobbled off after just 12 minutes, so there was always a nagging fear Joe Cole's failure to find the net when he robbed Patrice Evra to give himself a clear sight of goal was going to prove costly.
Chelsea, already given one let off when Petr Cech's wayward clearance gave first Dimitar Berbatov, then Wayne Rooney the chance to launch speculative efforts at the home goal, survived again when Rooney set up Ferdinand, only for the home keeper to save with his legs.
But on their next attack, United finally prospered as Patrice Evra galloped past Bosingwa to reach Rooney's inspired through ball.
Evra's pinpoint cross found Berbatov and while Cech was once again equal to the shot, Park had the easiest of tasks to bundle home the rebound.
After spending nearly half an hour on the back foot, Chelsea finally got into their stride.
Gary Neville's back header spread panic in the visitors' defence and when Edwin van der Sar came off worst in a collision with Florent Malouda, who might easily have scored, the veteran Dutchman was eventually forced from the field.
With Nicolas Anelka also firing over on a couple of occasions, it was not until the arrival of Didier Drogba that the home side really upped the ante.
Joe Cole should have done more with Anelka's low cross than prod it straight at Evra, then Jonny Evans - preferred to Wes Brown in central defence - got in the way of Bosingwa's shot.
Ferguson's response was to bring on Cristiano Ronaldo, who put the Chelsea defence on red alert with his direct running.
In ignoring Anelka's pleas for a pass as Ballack split United's defence wide open, Joe Cole needed to do better than blast his shot straight at Tomasz Kuszczak, who was quickly becoming one of the visitors' key men.
There would have been nothing the Pole could do to keep out Anelka's effort 18 minutes from time though as, from four yards out and with the goal at his mercy, the Frenchman inexplicably failed to make contact with Bosingwa's cross, the ball bouncing to safety off the Frenchman's standing leg.
But just as a wobbling Chelsea had eventually tumbled in the first-half, so United did the same 10 minutes from time.
In chopping down Ashley Cole, Rooney not only picked up his side's fifth booking. He also provided Mikel with the opportunity to float over a free-kick to the edge of the United six-yard box where the visitors, getting their marking and offside trap hopelessly wrong, left Kalou on his own to nod home the equaliser.
