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Sergio Aguero struck after just 19 seconds to put Manchester City firmly on course for the last 16 of the Europa League.

The Argentinian, who scored the winner in the first leg of their tie against Porto last week, showed great composure to extend the aggregate lead almost straight from kick-off at the rainswept Etihad Stadium.

Porto threatened at times but Aguero was unlucky not to put the tie beyond their reach when he hit the bar.

City boss Roberto Mancini made just one change as Aguero, who came off the bench to score the late winner as City won the first leg 2-1, replaced Mario Balotelli for the return.

Balotelli, the subject of alleged monkey chants at the Estadio do Dragao last Thursday, was on the bench alongside fellow forward Edin Dzeko.

The build-up to the game was overshadowed by Carlos Tevez's apology to Mancini for his recent conduct.

Tevez, who has not played for City since falling into dispute with the club began last September, returned to Manchester last week after an unauthorised three-month break in Argentina.

Mancini, who has not yet met the striker since he came back, was asked about the situation prior to kick-off.

The Italian told ESPN: "Tomorrow I will meet Carlos and talk with him."

On the pitch, City were soon into their stride.

The 5pm kick-off may have been a problem for some fans but the players raced out of the blocks to take the lead with just 19 seconds on the clock.

Aguero, who struck six minutes from time last week, started where he left off as he was played through by Yaya Toure and slipped the ball low past Helton.

City looked comfortable for their lead and could have had a second when David Silva beat the defence with a brilliant ball for Toure.

Helton rushed out of goal to meet the Ivory Coast midfielder on the edge of the box and spread his body to block his shot.

Porto enjoyed some spells possession and carved out a good chance for first-leg goalscorer Silvestre Varela but Joe Hart smothered his effort.

Porto continued to look for a way back into the tie and won a free-kick on the edge of the area but Joao Moutinho curled a shot over.

Aguero was unlucky not to score a second as he latched onto a long ball and headed it past the advancing Helton.

It left him at a tight angle wide on the left but his chip was almost perfect as it dropped onto the crossbar.

Porto continued to show their composure in possession but were unable to create meaningful chances, aside from a shot from Lucho Gonzalez which flew over.

The highly-rated Hulk tried to create problems but drove a cross across goal from a good position.

City spurned another chance to extend their advantage as they broke from deep and Aguero released Toure.

Toure appeared to have a good shooting opportunity but he checked back as cover arrived and Aguero drove wide.

Nicolas Otamendi missed the target as Porto went close just before the break.

HT: Manchester City 1 Porto 0 (Agg: 3-1)

The game remained open as the second half got under way with Aguero dribbling into the Porto box to tee up Silva but Maicon slid in to deny the Spaniard.

At the other end Gonzalez prodded an effort narrowly wide from 18 yards.

The Portuguese champions pieced together a nice passing move and Maicon drove the ball into the box but the offside flag was raised before James Rodriguez turned it into the net.

Hulk almost broke through as Porto attacked again but Samir Nasri got a foot in at a vital moment.

City again pressed for another with Silva winning a corner from Helton with a powerful drive before play was held up after Otamendi was accidentally kicked in the face by team-mate Maicon.

FT: Manchester City 4 Porto 0 (City win 6-1 on aggregate) City put the result beyond any doubt as substitute Dzeko, who had been on the field just seven minutes, was slipped in by a fine ball from Aguero and finished with confidence.

It proved a double blow for Porto as Rolando, who had been booked early in the game, was shown a second yellow card as City celebrated - perhaps for protesting too much for offside - and left the field.

City then went on to wrap up the game in style as Silva added a third after 84 minutes after substitutes David Pizarro and Dzeko combined to provide a tap-in.

Another followed two minutes later as Pizarro again linked up with Dzeko and broke into the box to slam past Helton for his first goal for the club.

INTRO: Manchester City produced a strong finish to power into the last 16 of the Europa League at the expense of 10-man holders Porto tonight.

Sergio Aguero set up victory by extending City's 2-1 first-leg lead after just 18 seconds at the Etihad Stadium before hitting the crossbar.

Edin Dzeko came off the bench to add a second late on before the sending off of Rolando preceded further goals from David Silva and David Pizarro.