JOIN USAlex Telles converted a VAR-awarded penalty deep into extra time as Porto defeated Roma 3-1 to reach the Champions League quarterfinal following a tense 4-3 win on aggregate.
Francisco Soares nudged Porto ahead with a simple tap-in on 26 minutes, but Daniele De Rossi equalised from the spot before half-time after Eder Militao chopped down Diego Perotti on Wednesday.
Moussa Marega restored the lead on the night for Porto early in the second half to level the tie as he struck in his sixth successive appearance in Europe.
An additional half-hour was required to settle an encounter that looked to be heading for a shootout before Telles tucked home from the spot on 117 minutes after a tug on Fernando by Alessandro Florenzi was spotted upon review.
"It was not just me that scored the penalty, it was the whole team. The Dragao, the full stadium, made me feel at ease. It was very good energy," said Telles.
"We've got to accept it, even if the way it happened is terrible to accept," Roma captain De Rossi told Sky Sport Italia.
Porto coach Sergio Conceicao, a former player at Roma's city rivals Lazio, had expressed the need for patience as his side set about attempting to retrieve a 2-1 deficit.
Yet they threatened twice inside the opening 10 minutes at the Estadio do Dragao as Jesus Corona hammered a volley narrowly over, with Telles lashing into the side-netting from a tough angle.
Corona again tried his luck from range, his shot again dipping over the top, and the Mexico winger was once more involved as Soares poked in the opening goal.
Marega, back in the side after missing the first leg with a thigh injury, pinched the ball from Kostas Manolas and was then picked out by Corona on the overlap to square for Soares to slot home.
Porto's lead lasted barely 10 minutes as Militao lunged in on Argentine Perotti, with De Rossi coolly rolling his penalty past three-time Champions League winner Iker Casillas.
Porto captain Hector Herrera, who was booked and will miss the quarterfinal first leg, tested Robin Olsen with a bending effort just before the break when Roma lost skipper De Rossi following a crunching tackle by Danilo.
Olsen was powerless to stop France-born Mali international moments later though as Marega timed his run perfectly to volley Corona's curling cross into the roof of the net.
With penalties seemingly on the horizon, Porto grabbed a dramatic winner after Turkish referee Cuneyt Cakir pointed to the spot upon reviewing an incident in which Florenzi hauled back Fernando as the substitute stretched to reach a driven low cross.
Telles sent Olsen the wrong way to fire Porto into their first quarter-final since 2014-15.