LISBON - Ricardo Quaresma claimed the winner just before the break to increase Porto's lead to seven points over Benfica on Saturday night at the Estadio da Luz.
The goal came when Lucho Gonzalez won the ball in midfield and fed Ricardo Quaresma.
He raced ahead of defender David Luiz and scored from just inside the penalty area to seal victory for the champions.
It was the first defeat of the season for Benfica, who are now a distant second although coach Jose Antonio Camacho remained defiant.
Camacho said: "We will keep working, we have to keep giving all we can."
Gonzalez revelled in Porto's win, saying: "We showed why we are the champions. There are still too many games before we can call ourselves champions again."
Porto coach Jesualdo Ferreira said: "We came to win in a stadium where Benfica had not lost in the last 30 games. It was a fair victory."
