Manchester City 4 Porto 0 (City win 6-1 on aggregate): Playing football in the late-afternoon drizzle, not to mention on Thursdays, is beginning to feel a little less comical than it seemed. Andre Villas-Boas, who was here to watch the side he made into reigning Europa League champions, could have been forgiven a twinge of envy for Roberto Mancini and for the spirit of European adventure which is beginning to take hold in the re-established capital of British football

There are four rounds of Europa League competition to play and many miles around lesser appreciated areas of the Continent to travel before the notion becomes reality, but few can resist at least discussing the prospect of this season of extraordinary Manchester rivalry going all the way to a Bucharest final between City and United on 9 May.

"That would be a good final, that," Sir Alex Ferguson said yesterday. "A good one for us," Samir Nasri had said, 24 hours earlier.

The fates must conspire in such an outcome, since there is an open draw from the quarter-finals on. But in three weeks' time, Manchester's may be the only European story the nation has to cling to and the two clubs are certainly showing a determination to collide.

Last night's match was certainly no foregone conclusion, flattering though the final scoreline looked. The defence Villas-Boas built in Portugal looked every bit as flimsy as the one he has fashioned at Chelsea, but the holders enjoyed considerable possession and forced two more of the fine saves which have made Joe Hart such a significant part of City's season.

Porto's hopes of a first win in England in 16 attempts were placed in perspective in the 19 seconds it took Sergio Aguero to put City ahead. Nicolas Otamendi's wayward ball out of defence was comfortably intercepted by Nigel de Jong, who found Yaya Touré for a gorgeous ball through Porto's central defence which Aguero drilled home for his 20th goal of the season. It is a little premature in the Europa League's undistinguished history to talk of its history men, though only an AEK Athens striker, Ismael Blanco, has scored a faster goal in the tournament.

The Portuguese champions were not without a threat, especially with the Brazilian Hulk piling in dangerous, low-driven crosses. But they did not have a notion of how to deal with the drenched and muddied figure of Aguero. Rolando hacked at him and was booked. The goalkeeper, Helton, ran at him as he advanced to take a lofted pass that David Silva played after intercepting another lazy ball. Aguero nodded the ball beyond him and clipped it back over Fernando and on to the underside of the bar.

City were prepared to sit deep in the first half and damage their visitors on the counter-attack, though to judge by the assistant manager David Platt's half-time comments this seemed to be more accident than design. If others had been as sure-footed as Aguero, they might have been three ahead in any case. Nasri took a touch when he should have lifted a ball which Helton's block took to his feet. Touré decided to funnel the ball back to Aguero, five minutes from the interval, when he should have shot. This time, the Argentine blasted over.

Porto flickered after the break. James Rodriguez's effort from Maicon's low cross before the hour was only marginally offside and Touré's booking for a hack at Joao Moutinho ensured that he will miss the first leg of the last-16 tie. But Aguero again instilled a sense of the indomitable in his side – foraging for a ball exchanged with Silva before playing in the unmarked Edin Dzeko for his 17th of the season.

Rolando's sense of injustice – he believed, wrongly, that Dzeko was offside – saw him dismissed for a second caution. Then there unfolded a fine, 10-minute cameo from David Pizarro, City's loan signing from Roma, who seized on another sloppy piece of Porto defence, exchanged passes with Dzeko and cut the ball back for Silva to score. An intricate move on the edge of Porto's box involving Pizarro and Dzeko then led the Porto substitute Christian Sapunaru to skew the ball into Pizarro's path, and he finished things.

The night ended with Joleon Lescott suggesting City have missed Carlos Tevez at times and with Mancini, who will meet his errant striker today, raising the prospect of the Argentine's return in three weeks. But from this vantage point that much-vaunted apology seemed academic, his services unrequired. City mean business – in afternoon drizzle or otherwise.

Man of the match Aguero.

Match rating 7/10.

Referee W Stark (Germany).

Attendance 39,538.