Ricardo Costa smashed in a second-half leveller for Porto but the Champions League holders face a tough second leg in the San Siro in three weeks. The Portuguese defender crashed home from two yards after Costinha diverted Ricardo Quaresma's deep cross to him.
Obafemi Martins side-footed Inter ahead after Dejan Stankovic powered into the box and crossed into the six-yard area.
Inter keeper Francesco Toldo tipped Maniche's shot over while Porto's Vitor
Baia saved Estaban Combiasso's volley.
Porto enjoyed the majority of possession in the first half but were forced to resort to long-range shots which Toldo dealt with comfortably.
Ricardo Quaresma fired in the game's opening shot after cleverly turning Inter's Cristiano Zanetti, but his low curling drive was held by Toldo.
The visitors, encouraged by their defensive control, became more adventurous - Marco Materazzi saw his goalbound header from Juan Sebastian Veron's free-kick acrobatically saved by Baia, while Adriano screwed a shot wide.
Porto's defence meanwhile continued to play high up the field and they were made to pay when Martins finished off a pacy Inter attack.
Stankovic collected the ball on the left and held off the challenge of Giourkas Seitaridis before delivering a low pass into the six-yard box to the unmarked Martins who tucked the ball home.
Maniche fired in a 25-yard dipping volley which Toldo tipped over the bar, while Luis Fabiano and Benni McCarthy failed to hit the target from outside the box as Porto struggled to create any clear-cut chances.
Toldo again denied Porto as the home side opened the second-half on the attack.
The Italian stopper held a low Seitaridis drive, but he was at fault for Porto's equaliser.
Quaresma swung over a deep cross from the left which Toldo misjudged and as the ball dropped over his out-stretched arm, Costinha pushed the ball back into the goalmouth for Costa to gleefully smash into the roof of the net.
Baia kept the scores level late on with two fantaastic saves.
First he stood up well as Martins raced into the box and deflected his effort wide and from the resulting corner, he parried Combassio's spectacular bicycle kick to keep the tie interestingly poised after the first-ever game between these sides.
Porto boss Jose Couceiro:
"Inter have the advantage but we still have a chance of qualifying. "They defended well and scored from an error on our part - we had control of the match but we played with the heart and not with the brain."
Inter boss Roberto Mancini:
"Inter played very well even if we could have won. "We could have won 2-1 but I say 'bravo' to Vitor Baia. They have a good team."
FC Porto: Vitor Baia, Pedro Emanuel, Ricardo Costa, Costinha, Nuno Valente, Quaresma (Postiga 83), Bosingwa (Luis Fabiano 28), Maniche, Seitaridis, Raul Meireles, McCarthy.
Subs Not Used: Nuno, Pepe, Leandro, Claudio, Paulo Machado. Booked: Costinha.
Goals: Ricardo Costa 61.
Inter Milan: Toldo, Cordoba, Javier Zanetti, Cristiano Zanetti, Adriano (Vieri 80), Veron (Emre 70), Favalli, Cambiasso, Materazzi, Stankovic, Martins.
Subs Not Used: Carini, Burdisso, Van der Meyde, Mihajlovic, Gonzalez.
Booked: Favalli, Cordoba, Materazzi.
Goals: Martins 24.
Att: 38,177
Ref: Graham Poll (England).
MMIX
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