Colombia forward Martinez took his tally to 10 in the league this season after finding the target twice in the first half-hour on a chilly night in Coimbra where only three Portuguese players featured among the 22 starters.
Porto went ahead after 13 minutes when Academica lost possession and Ruben Neves found Martinez who, under little pressure, struck from the edge of the area.
Martinez added another 11 minutes later after an Academica move broke down. Mexican Hector Herrera completed the scoring three minutes after the break as Porto, second with 28 points, made it eight goals from two games.
Benfica, three points ahead of their great rivals, struggled to break down Belenenses who nearly grabbed the lead in the 20th minute when Tiago Caeiro's header was parried by Brazil goalkeeper Julio Cesar.
The Eagles finally broke through in the 64th minute when Lima headed in from close range after the ball took several ricochets in the area.
Argentina midfielder Enzo Perez converted a penalty six minutes later and compatriot Eduardo Salvio nodded the third goal after a superb run by Nicolas Gaitan.
(Writing by Brian Homewood, editing by Tony Jimenez)
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