Two goals by Brazilian striker Derlei Silva helped Porto come from behind to crush Lazio 4-1 in their UEFA Cup semi-final, first-leg clash on Thursday.

The superb victory, achieved in pouring rain, put the Portuguese league leaders firmly on course for the final in Seville on May 21, where they would either face city rivals Boavista or Scotland's Celtic.

Boavista drew 1-1 at Celtic on Thursday and if the two Oporto-based teams emerge victorious after the second legs, it will be the first time two clubs from the same city have reached a major European final.

Lazio's Argentine Claudio Lopez caught Porto cold in the sixth minute when he sneaked inside the area to pick up a cross from the left by Cesar and blast the ball past Portuguese international keeper Vitor Baia.

But Porto, the 1987 European Cup winners, hit back quickly on a wet pitch.

Playmaker Deco Souza was well positioned in front of an open goal soon after but could not quite reach a cross by Derlei.

In the 10th minute Derlei found Maniche Ribeiro 20 metres out and he equalised with a deft lob over the Italian visitors' goalkeeper Angelo Peruzzi.

Deco set up Porto's second goal in the 27th minute by winning a corner and then floating the set piece over for Derlei to head home.

HEAVY RAIN

Baia had little to do as Porto created nearly all the remaining chances in the first half, with both Derlei and team mate Helder Postiga shooting just wide.

The home crowd, braving heavy rain in the open-air Antas stadium, then roared in anger when Derlei fell inside the area after a challenge by Lazio defender and Porto old-boy Fernando Couto only for Greek referee Kyros Vassaras to wave away the shouts for a penalty.

Porto did not have to wait long for their third goal, though, as Peruzzi dropped a long-range free kick early in the second half and was too slow to prevent Derlei from running in to score from close range.

The home side were rampant and made it 4-1 in the 56th minute. Russian midfielder Dmitri Alenichev produced a fine run down the right and found Postiga who scored from inside the area.

Play again went Porto's way in the rest of the game and many of the sodden home supporters felt confident enough to leave early.

Lazio captain Giuseppe Favalli forced a corner but Sinisa Mihajlovic gave the set piece straight to Baia and substitute striker Simone Inzaghi sent a rare shot wide of Porto's left post.

Defender Nuno Valente threatened to grab a fifth for Porto from 20 metres out while Deco also came close with another free-kick, which he sent just past the right post.