Manchester City's record signing came off the bench to score twice and set up another in the final 30 minutes as Mancini's men began their league campaign with a 4-0 thrashing of promoted Swansea.

Aguero was an unused substitute for last week's Community Shield and was again kept waiting until after Edin Dzeko had finally broken Swansea resistance just before the hour at the Etihad Stadium.

The Argentinian immediately made up for lost time by sliding in a Micah Richards cross and skilfully setting up David Silva before crowning a remarkable bow with a stunning 30-yard drive.

It was a victory City thoroughly deserved after hitting the bar twice through Silva and Gareth Barry in the first half and forcing numerous saves from Michel Vorm.

Manager Mancini said: "I know Aguero very well but I don't think he is 100%.

"He has worked for only one week with the team.

"He needs to improve but he is a fantastic striker and I am happy because he scored two important goals."

Mancini was pleased to get a campaign in which his side are expected to challenge for the title off to a winning start.

He added: "It was the perfect start. It was important to start the season very well and it was important to score the goals and score with the strikers."

Mancini left controversial striker Mario Balotelli on the bench and wantaway Carlos Tevez was not even in the squad.

Balotelli has had a number of run-ins with Mancini recently and Tevez's future remains the subject of speculation, but the City boss wants to make full use of both players.

"We have four important strikers and they can play together," said the Italian. "I think Carlos will stay here."

Mancini is expected to strengthen his resources further by bringing in Arsenal's Samir Nasri but yesterday refused to speak on the subject.

For Swansea, promoted after a thrilling play-off win over Reading, their Premier League bow was a harsh reality-check.

The Welsh side competed well in the first half-hour but after that were outplayed as the hosts upped the tempo.

But manager Brendan Rodgers: "I thought overall the result - although there were some fantastic goals - was harsh on our team.

"You come off the pitch having been beaten 4-0 but I said to the players, 'Congratulations, you have put on a terrific show tonight'.

"We showed we can be a threat in this league and we will take all the positives from this game and go again on Saturday."