Porto dominated the first half with Martinez denied from four yards out by a brilliant save from Pepe Reina.
The impressive Carlos Eduardo then headed in from close range after Martinez’s cross but it was wrongly ruled out for offside.
Porto, the 2011 Europa League winners, began the second period well with Reina tipping over Fernando’s long-range effort.
Helton was then called into action after saving Gonzalo Higuain’s low shot and then Raul Albiol’s header.
But Porto took the lead on 57 minutes when Martinez’s low strike deflected into the net following a corner.
Substitute Juan Quintera hit the post late on as Porto take a one-goal lead going into the return leg next Thursday.
10’ – GREAT SAVE: What a save by Reina! Eduardo's cross found Martinez four yards out and his shot was tipped over.
20’ – DISALLOWED GOAL: Eduardo heads into the net from a yard out after Martinez’s cross but is ruled out for off-side. Replays showed he was level.
46’ – REINA SAVE: What a strike! Fernando lashes in a first-time effort from 30 yards which Reina tips over.
53’ – GREAT SAVE: From the corner, Albiol's header was parried by Helton at point-blank range.
55’ – GILT-EDGED CHANCE: How did Napoli not score? After Higuain beat Mangala with ease, he shoots across goal and Callejon can only divert it wide with the goal at his mercy.
56’ – GOAL! Following a corner, the ball falls to Martinez’s whose fizzing shot deflects into the bottom corner.
81’ – WOODWORK: Porto hit the post after a brilliant tackle from Britos to deny Quintero.
82’ – CHANCE: Maicon clears off the line from substitute Zapata diverting the ball towards goal.
90’+2 - CHANCE: Zapata fails to get a touch to Pandev's cross, a great chance for a late equaliser. KEY STATS
The win was Porto’s first victory at home in five matches.
Napoli have now won only one of their last 10 Europa League matches on their travels.
Marek Hamsik has not found the net for Napoli since November.
TALKING POINT: Should Liverpool bring back Pepe Reina next season? The keeper is on loan at Napoli and gave an outstanding performance. He made two world-class, point-blank saves and his distribution was brilliant. He is only 31-years-old and the Reds’ Simon Mignolet has made a few errors this season.
MAN OF THE MATCH
Pepe Reina: The keeper made outstanding saves to deny Jackson Martinez and Fernando. He could do little about the goal.
Porto: Helton 7, Danilo 7, Maicon 6, Mangala 5, Sandro 6, Quaresma 6, Defour 6, Fernando 7, Eduardo 7, Varela 6, Martinez 8. Subs: Quintero 6, Ghilas 5, Herrera 5.
Napoli: Reina 9, Reveillere 6, Albiol 7, Britos 6, Ghoulam 5, Callejon 6, Henrique 5, Behrami 5, Insigne 5, Hamsik 5, Higuain 6. Subs:, Mertens 5, Pandev 6, Zapata 5.
MATCH IN A TWEET
- Sports & Recreation
- Pepe Reina
- Europa League
- Jackson Martinez
- Gonzalo Higuain