Paulo Fonseca's side responded to going in at the break a goal down, as strikes from Nabil Ghilas, Lica and a Federico Fernandez own goal produced a two-goal winning margin
Despite holding a half-time lead courtesy of Goran Pandev’s penalty, the Serie A outfit succumbed to three strikes after the break from Nabil Ghilas, Lica and an own goal from Federico Fernandez.
Each side made nine changes to the starting XIs sent out on Saturday, ensuring those watching in the stands and at home took in essentially two different teams for the majority of the encounter.
Sadly for Porto, this did little to change their fortunes in the opening 45 minutes, bar some lively moments from the precocious Juan Quintero, whom big things are predicted. Otherwise, plenty of possession was overshadowed by a more incisive Partenopei.
Pandev again led the line for Rafa Benitez’s side and gave Eliaquim Mangala and Nicolas Otamendi problems from as early as the 10th minute. The Bulgarian latched on to a pinpoint through-ball from Dries Mertens only to dally just long enough for Otamendi to recover and block.
Alessandro Gamberini came close with a header moments later, but Napoli’s threat was again carried by Pandev as he surged off the right flank, beyond two defenders, finally striking into Helton’s hands.
Porto grew into the half but were undone by the Anthony Taylor’s whistle as Fernando’s nudge on Pandev was considered aggressive enough for a penalty - the fifth in two and a half games in north London. This left the lively Pandev to open the scoring as he cooly sent Helton the wrong way from 12 yards.
Quintero gave yet another hint of his potential, bookending the half with a powerful free kick that sailed just wide of the near post, but for the Dragoes there was barely a hint of an end product.
As boos rang around a half-full Emirates Stadium - signifying Gonzalo Higuain’s introduction at half-time - it was difficult to imagine a way back for Paulo Fonseca’s side.
And yet, all of a sudden Ghilas came into view after a quiet first period. The Algerian, brother of former Hull forward Kamel, looked to have found an equaliser in the 48th minute but stabbed Alex Sandro’s cross just wide.
Moments later, though, he found the back of the net with a calm sidefoot past Rafael. The credit, though, would go to Quintero, whose electric run from the right and surgical through-ball released Ghilas.
Just after the hour mark Ghilas again found room in behind Andrea Dossena as the 23-year-old sprung the offside trap near the halfway line. His low cross found Fernando, but the midfielder could only prod into the side-netting.
With the scores level, Helton was called into action, producing two splendid saves from Jose Callejon and Juan Zuniga - the first a low fingertip effort, the second, from the rebound, a reflex save from close range.
Porto began to look increasingly dangerous on the break and Silvestre Varela sent a demon of a cross into the box from the right that Fernandez clumsily turned beyond his own goalkeeper.
Fonseca’s side had the lead and faced surprisingly little resistance as the game lurched into its latter stages.
A cute chip over the defence from substitute Juan Iturbe released Lica, another sub, and although the summer signing made a mess of bringing the ball under control, he was left grateful to Dossena for squaring an attempted pass right at the Portuguese’s feet.
Lica made no mistake from 10 yards, giving Porto an unassailable lead and a deserved victory.