Aguero was 19 when he played for Atletico Madrid against Bolton in a UEFA Cup tie in February 2008, coming off the bench in the second half but lasting just 12 minutes before he was sent off for spitting at Bolton's Matt Taylor.
He could not have imagined then that his next appearance there would be for City, currently sitting joint top of the Premier League alongside Bolton - albeit after one match - after both produced 4-0 wins in their season-opening games.
Bolton scored their emphatic victory at promoted Queens Park Rangers while City beat another promoted team, Swansea City, by the same score at home on Monday when Aguero came off the bench to score twice.
Along with champions Manchester United and Wolverhampton Wanderers, they are the only four teams with maximum points after the opening games, although Tottenham Hotspur and Everton are yet to play.
Their match at White Hart Lane was postponed last week because of the London riots with Spurs not starting their League campaign until Monday when they visit United. Everton kick off their season at home to QPR on Saturday.
In other key games this weekend, Arsenal, facing up to life without the departed Cesc Fabregas and probably Samir Nasri who seems set for a move to City, face Liverpool.
The Gunners, who also have Gervinho and Alex Song suspended following last weekend's bad-tempered draw at Newcastle United, are at home, with both sides on one point after the Merseysiders' draw with Sunderland last Saturday.
Chelsea will be without goalkeeper Petr Cech for three or four weeks after the keeper suffered a knee ligament injury but will be looking for their first win after last week's 0-0 draw at Stoke City. They play West Brom at Stamford Bridge.
While all the title challengers will be concentrating on their own games, they will also be keeping a close eye on City, who demolished Swansea with a fine performance on Monday night at the start of a campaign they hope will end with their first league title since 1968.
Aguero, who since that night at the Reebok three-and-a-half years ago has matured into a world-class player, said he remembered the incident well.
The 23-year-old Argentine striker recalled: "I spat in the direction of the player but not at the player himself.
"However, the officials thought I had, and they suspended me. I don't know what it will be like when I go back, but hopefully I can make City's supporters happy," he told the Manchester Evening News.
He certainly made them happy on Monday when he came off the bench at around the same time as he had against Bolton, but this time scored two goals on his first appearance since becoming City's record 38.0 million pounds signing.
The first was an opportunistic close-range effort, the second a thunderous 30-metre drive. His performance drew lavish praise from the media and his manager Roberto Mancini, who said he was already a fa
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