Paris St-Germain secured top spot in Champions League Group A after a second half error by Porto goakeeper Helton handed the French side a 2-1 win at the Parc des Princes.
PSG made their early pressure count when captain Thiago Silva beat Helton with a bullet header approaching the half-hour mark.
Porto levelled soon after through Jackson Martinez’s close-range header, but PSG sealed the win when Ezequiel Lavezzi's tame shot squirmed under Helton's body at his near post.
With Dynamo Kiev having already secured a Europa League place ahead of Dinamo Zagreb, the only matter at stake in the French capital was who topped Group A. PSG needed all three points, while Porto would win the group with just a draw.
That pressing need for a victory seemed to resonate with Carlo Ancelotti’s side, who pinned Porto back in the early stages, with a full-stretch Zlatan Ibrahimovic unable to make clean contact with Javier Pastore’s low cross after a slick PSG counter-attack.
Porto showed little interest in gaining anything more than the point they needed from Paris, and the Portuguese champions allowed Ibrahimovic another sight of goal, as he volleyed wide at the far post.
But the PSG pressure, and a succession of corners, eventually told when Silva stole a yard in the box to power a header beyond Helton after Maxwell delivered a pinpoint free-kick.
But PSG were celebrating for barely four minutes. Porto reacted well to conceding, and Danilo exploited a sea of space afforded him by Maxwell on the Porto right. His perfect cross found Martinez at the far post, and his stooping header found the roof of the net to make it 1-1.
Joao Moutinho, a possible January transfer target for Tottenham, whose coach Andre Villas-Boas was in attendance at the Parc des Princes, began to exert his influence on the remainder of the half, as PSG struggled to contain a renewed Porto side.
But half-time came at the wrong time for Porto as PSG, inspired by the superb Pastore, wrestled back control of the game in the second half. PSG could have gone ahead when Pastore released Jeremy Menez with an inch-perfect through ball, but Menez was denied at the last moment by the excellent Nicolas Otamendi.
PSG continued to press and Menez again came close when he cut in from the left, but was kept out by a superb point-blank save by Helton. But no sooner had Helton kept Porto in it, he was at fault for what proved the winner.
Collecting the ball in the box, Lavezzi tried his luck with a low shot from an acute angle that Helton had appeared to have covered, only for the ball to go under the Brazilian’s body.
Porto pushed for an equaliser but, when their best chance fell to Martinez, he was denied by Salvatore Sirigu, who raced off his line to smother the shot brilliantly – and then watched with relief as Porto captain Lucho Gonzalez fired the loose ball over from 20 yards.
That was as good as it got for Porto in the second half as Ibrahimovic and Pastore spurned late chances to put the gloss on the win. But it mattered little as the French side progressed to the last 16 as group winners, relieving some pressure that had been building on Ancelotti.
MAN OF THE MATCH
Javier Pastore - PSG: A livewire in attacking midfield, the Argentine created chances all night and was unlucky not to be on the score sheet himself.
PSG: Sirigu 8, van der Wiel 8, Alex 7, Thiago Silva 8, Maxwell 8, Matuidi 7, Chantome 7, Pastore 9, Menez 8, Lavezzi 7, Ibrahimovic 6. Subs: Verratti n/a, Jallet n/a, Nene n/a.
PORTO: Helton 6, Danilo 7, Otamendi 8, Mangala 6, Alex Sandro 7, Fernando 6, Lucho Gonzalez 6, Moutinho 8, Rodriguez 7, Varela 5, Martinez 7. Subs: Defour 6, Atsu n/a, Ba n/a.