Benfica lost 3-4 at home to Santa Clara which saw the islanders score a winner in added time. It gives Porto the chance to go three points clear of Benfica.
The team from the Azores were winning 0-1 at half-time thanks to a goal from the Brazilian midfielder Anderson Carvalho.
In the second half, Rafa Silva levelled things up for the hosts, but they fell behind again in the 57th minute. Zaidu Sanusi scored for Santa Clara.
However, Carlos Vinicius, who came on for Haris Seferovic, scored in the 63rd and then again a minute later to but Benfica 3-2 up. Vinicius is now the top scorer in the Portuguese league with 17 goals.
Santa Clara did not give up though and the Brazilian left winger Crysan drew the away side level after 82 minutes at the Estadio da Luz.
Then, in the 95th minute, Ze Manuel gave Santa Clara a last gasp winner and made it 3-4 to give the visitors a vital win.
Porto face Boavista later on Tuesday and the home side have the chance to go three points clear of Benfica.
In the other early game, Setubal lost 1-2 at home to Rio Ave, who are fifth on 44 points, three behind Braga. Braga are currently in the final Europa League spot.