Manchester City FC will already be glimpsing themselves in the last 16 after Sergio Agüero's late goal capped a 2-1 comeback success to ruin FC Porto's return to the UEFA Europa League.
Winners of this competition last season, Porto went ahead through Silvestre Varela close to the half-hour as their slick passing made them a thorny proposition. Roberto Mancini's men were creating danger of their own, though, and Álvaro Pereira's own goal brought them level after the restart before substitute Agüero finished from close range with five minutes remaining.
The hosts made the first inroads of a tight opening period and went close after 15 minutes when Gaël Clichy was forced to head a Rolando header over the crossbar following a corner. That scare brought a rapid response from City, with Helton batting away a Samir Nasri free-kick so nearly diverted by Mario Balotelli, before the goalkeeper dived to his left to deny Micah Richards and Nasri.
Having finally made their presence felt, the visitors promptly fell behind, as Hulk broke free down the left and rifled in a low cross for Varela to stab in ahead of Clichy. Helton's save from a long-range Balotelli half-volley preserved the advantage, the Italy striker having had time and space to run at goal, and a wayward Hulk effort ensured it was not extended before the break.
Taking heart from their first-half openings, City turned up the tempo after the interval, with Richards blasting against a post before Álvaro Pereira turned a searching Yaya Touré ball into his own net under pressure from Balotelli.
It was then Joe Hart's turn to impress between the posts as he pawed away a swerving Hulk set piece, and it was Helton who conceded next as Touré fed Agüero from the left to leave the visitors on top ahead of next Thursday's reunion.