Manchester City came from behind to beat defending champions Porto 2-1 at Estadio do Dragao on Thursday and take a sizeable step towards the UEFA Europa League last 16.
A late goal from substitute Sergio Aguero completed a precious away win for Roberto Mancini's side and condemned Porto to their first home defeat in European competition in eight games. Silvestre Varela had given Porto the lead midway through the first half, but Alvaro Pereira's 55th-minute own goal drew the Premier League leaders level before Aguero secured victory with six minutes to play.
Having emerged from one of Europe's most daunting away grounds with victory, not to mention with two away goals, City will be favourites to progress ahead of the second leg at Eastlands next Wednesday.
"I think that we played a good game," City coach Roberto Mancini told ITV. "We played very well. In the first half we had three or four chances to score and we were really unlucky. In the second half we played really well.
"We had several chances to score in this game and we didn't leave chances to Porto. That's important, because Porto are a good team."
Porto have fallen five points behind eternal rivals Benfica in their defence of the Portuguese league title, but they made a confident start and saw Rolando's header diverted over the bar by City left-back Gael Clichy after 15 minutes' play.
However, their momentum was disrupted by an injury to Danilo that saw the Brazilian right-back stretchered off on his European debut for the club, and City briefly looked set to take advantage. Home goalkeeper Helton had to push a dipping Micah Richards half-volley around his left-hand post and moments later Samir Nasri shot straight at the Brazilian goalkeeper after being freed by David Silva.
Having survived those scares, Porto gathered themselves together and took the lead moments later, with Varela getting in front of Vincent Kompany at the near post to touch home Hulk's low left-wing cross. City threatened to hit back immediately, but Mario Balotelli, back in the side following a four-game domestic ban, rushed his shot after Nasri picked him out behind the Porto defence and Helton was able to save.
The visitors signalled their intent early on in the second half when Richards hit the post after a typically marauding run down the right flank, and five minutes later they were level. There appeared to be little danger as Yaya Toure lofted a pass towards the Porto penalty arena, but Balotelli's shove threw Pereira off balance and the Uruguayan international unwittingly diverted the ball past Helton with his shoulder.
Porto had 35 minutes to restore their advantage, but City had little difficulty keeping them at arm's length and in the 84th minute they stamped their authority on the tie with the winning goal. Toure strode into the penalty area and squared for Aguero, who had the simple task of tapping the ball into an empty net from eight yards.