The Reds No.10 initially appeared to be offside when he converted Mohamed Salah’s knock across the box midway through the first half – but a Video Assistant Referee review correctly confirmed he had been onside.
Mane’s breakthrough halted a dangerous passage of play by the hosts at Estadio do Dragao and led to an ultimately emphatic victory for Jürgen Klopp’s men in the last-eight second leg.
Salah, Roberto Firmino and Virgil van Dijk also found the net after the interval to seal a 6-1 aggregate result, with Eder Militao providing a consolation for Porto.
“I was thinking it was offside, to be honest,” Mane told BT Sport when asked for his take on the 26th-minute opener.