Needing a point to prevent Benfica from wrapping up the trophy, Porto overcame an early penalty miss by Ricardo Quaresma and Martinez, the league's top-scorer, took his tally for the season to 20.
Benfica, who thumped bottom club Penafiel 4-0 on Saturday, stayed three points clear at the top with two games left and remain firm favourites to retain the title.
The mercurial Quaresma wasted a chance to give Porto the lead when his penalty was superbly saved by Adriano after 10 minutes.
However, the ball came immediately back into the Gil Vicente area and Yacine Brahimi crossed for an unmarked Martinez to head Porto in front at the far post.
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The Colombian completed the win in spectacular style with four minutes to play, albeit helped by slack marking.
A low, hard cross was played in from the right and Martinez, with his back to goal, flicked the ball into the air and scored with an overhead kick.
Benfica, who have a better head-to-head record against Porto, need three more points to wrap up the title but they have a tricky game at Vitoria Guimaraes next weekend.
"This team has already done a lot of good things this season, it's a team with a lot of soul," Porto coach Julen Lopetegui told reporters.
"We have played 50 matches this season, 12 of them in the Champions League, and the team continues to work hard and believe. We will keep going to the end."
(Writing by Brian Homewood in Berne, editing by Ed Osmond)
