Roma 3 Chelsea 1:Montenegro striker Mirko Vucinic blew Group A wide open at the Olympic Stadium as his two second half goals earned the Serie A strugglers a convincing victory.
Former Chelsea star Christian Panucci got Roma's opener after 34 minutes. Despite John Terry getting a goal back the night was to end in further misery for the Premier League leaders when Deco was sent off after receiving a second yellow card for taking a quick free-kick with ten minutes to go.
A cagey start from both sides was brought to an end when Deco tried his luck from 25 yards but the Chelsea midfielder was thwarted by a fine save from Doni.
Moments later Vucinic was just off target with an 18-yard volley that failed to trouble Petr Cech.
A clever run down the left flank by Florent Malouda should have resulted in a clear opening for Nicolas Anelka but he just failed to connect with the pass.
Chelsea were having the best of the opening exchanges with Frank Lampard and Deco controlling the game in midfield.
Another run down the left by Malouda provided Deco with a second chance to open the scoring but this time his 20-yard effort was deflected for a corner.
But for all their initial domination, they could not convert their superiority into goals.
Lampard, a clear thorn in Roma's side, forced Doni into a fine save by his near post when he let fly from 20 yards in the 21st minute.
On the half hour Deco set up Lampard for another shot of goal but the England midfielder was again denied by the agility of Doni in the Roma goal.
Roma had posed little threat to the English side but a poor pass from John Mikel Obi forced Deco to bring down Francesco Totti resulting in a yellow card.
Chelsea paid a heavy price for Deco's misdemeanour as Roma went ahead in the 33rd minute through Panucci.
Cicinho's pass from the right wing eluded everyone when Panucci reacted first to sweep the ball into the net from close range.
It was a goal scored completely against the run of play but struggling Roma took heart from their good fortune and began to boss the game.
In the 37th minute another crude challenge by Obi, this time on Matteo Brighi gave Roma another chance to increase their advantage but Cech saved well from Totti.
Malouda then wasted a chance to equalise two minutes later when he sent his effort wide of the target from 20 yards.
Chelsea boss Luiz Felipe Scolari made two changes at half-time, replacing Joe Cole and Malouda with Didier Drogba and Juliano Belletti.
But the changes had little time to take effect before Vucinic put Roma two in front three minutes after the break.
The Roma midfielder took a short pass from Brighi and sent a rising 25-yard drive into the net beyond the despairing Cech.
Roma went three in front on 58 minutes when Mikel made another error. The Nigerian lost the ball to Vucinic who ran the length of the Chelsea half, then beat the retreating Mikel again before firing home beyond Cech.
In the 62nd minute Chelsea replaced Jose Bosingwa with Salomon Kalou in a vain attempt to haul themselves back into the game.
Chelsea had bossed the game in the early stages but two catastrophic errors from Mikel had sent them hurtling towards a heavy European defeat for some years.
In the 66th minute, Drogba tried to pull one back with a long-range free-kick but the ball went straight into the arms of Doni.
Chelsea looked down and out but grabbed a lifeline 15 minutes from time when Terry pulled a goal back.
The Blues skipper chested Deco's shot towards goal and, after it was saved by Doni, slotted the rebound home as Roma's players appealed in vain for offside.
But just minutes later the visitors were reduced to 10 men in comical circumstances when Deco was shown a second yellow card, seemingly for taking a free-kick too quickly for the referee's liking.
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