Title holders Porto produced a dramatic comeback to edge into the knockout phase of the UEFA Champions League after a 2-1 home success over Chelsea.

Jose Mourinho, who took Porto to the European crown last season, looked primed to dump his old side out of the competition after Damien Duff's first half opener at Estadio do Dragao.

Diego's brilliant volley on the hour mark to level would still have been insufficient to claim the runners-up spot in Group H until Benni McCarthy's header five minutes from time sent Porto through, along with Chelsea, at the chief expense of CSKA Moscow.

Porto, in pursuit of the required win, did not lack ambition in the early stages with Greek full back Giourkas Seitaridis shooting tamely from 35 yards at Petr Cech.

Chelsea responded with Duff's pass along the edge of the area prompting Frank Lampard to display the technique of a schoolboy as he completely missed the ball, before Wayne Bridge shot wide.

Lampard then showed the expert nature of his ability with a superb cross which was met by Didier Drogba but his header from six yards out was pushed magnificently onto the bar by Nuno.

The reigning champions struggled to put the visitors under any pressure with Benni McCarthy curling a free kick wide and Derlei poorly volleying over the bar.

The Blues twisted the knife on 34 minutes via a goal Porto keeper Nuno will not look back on fondly. Duff cleverly cut inside from the right and unleashed a swerving shot which flew past Nuno's lily-livered attempt at a save.

Nuno's opposite number Cech, rather than the Porto forwards, was causing the Chelsea defence most concern as he flapped at a couple of crosses in a first half which enabled the Premiership side to happily go through the motions.

There was a distinct lack of quality on show in the opening 15 minutes of the second period before Brazilian starlet Diego raised the level with a stunning equaliser on the hour.

John Terry could only partially clear a shot to the edge of the area where, lurking menacingly, Diego unleashed a rasping volley beyond the static Cech.

The Chelsea keeper then continued his uneasy display by dealing poorly with a shot from the far edge of the area by McCarthy as Porto scented a winner.

Lampard had a great chance to restore Chelsea's advantage on 74 minutes but sidefooted meekly at Nuno when he should have pulled the ball back to the waiting Drogba.

With any prospect of retaining the trophy seemingly slipping from Porto's grasp, they conjured up a well-crafted winner with five minutes remaining.

Substitute Ricardo Quaresma delivered an excellent cross from the left wing to the far post and McCarthy timed his leap to perfection to plant a header beyond the diving Cech.

For much of the game Porto never looked likely, or deserved, to advance to the second round but, with fortune on their side, they will now be aspiring to back-to-back titles, a dream shared by their former coach Mourinho with his current team Chelsea.