Sergio Aguero took the Premier League by storm with a two-goal half-hour cameo on his Manchester City debut and rival teams must now be dreading what the striker can do in a full game when fully fit.

A 4-0 thrashing of Swansea City Monday was the perfect start to the season for the title aspirants and Aguero's impact from the bench had the home crowd in raptures even if ice-cool Italian manager Roberto Mancini took it in his stride.

"What Sergio Aguero achieved did not surprise me," Mancini told reporters.

"He is a fantastic striker. However, he can get better than he showed against Swansea. I am sure of that. He is not yet 100 percent fit. He only has 10 days training with us and he will get better."

The 23-year-old Aguero, a record signing even for mega-rich City having cost a reported $64 million, was supposed to be still feeling his way back after being one of the few success stories for Argentina at the recent Copa America.

Instead he paid back some of the fee straight away and burst onto to scene like an English veteran, immediately in tune with the pace of the game and his team mates when coming on as a substitute after Edin Dzeko's 57th minute opener.

"Kun" almost scored with his first touch and while his first goal after 68 minutes was a tap-in, his positioning at the far post was the hallmark of a striker who plays through instinct.

His athleticism and drive were then displayed when he somehow kept the ball in play having danced around the keeper before hooking it back perfectly for David Silva to score.

Aguero's third and City's fourth in stoppage time against promoted Swansea showed his sheer class as he found the corner from distance with a rasping effort that his father-in-law, Argentina great Diego Maradona, would have been proud of.

Aguero was bought from Atletico Madrid as a replacement for Carlos Tevez with his countryman wanting a move, but no transfer looks likely before the August 31 deadline and Mancini could have the luxury of fielding them both at Bolton Wanderers Sunday.

"Aguero could play with Tevez or any of the other strikers," said Mancini, whose side have quickly recovered from their late Community Shield loss to rivals Manchester United.

"Carlos at this moment is still our player and maybe he will be available for the game at Bolton."