Manchester City capitalized on Laurent Koscielny's early sending-off to canter to a first league victory at Arsenal in 38 years, with Sunday's 2-0 win keeping the defending champions seven points behind Manchester United in the Premier League title race.
The France center back was shown a straight red card for rugby-tackling Edin Dzeko to the ground inside the area, leaving Arsenal a man down with just nine minutes gone.
Dzeko's resulting penalty was saved - via the post - by Wojciech Szczesny, but the Bosnia striker made amends by adding to James Milner's opener to give City a 2-0 lead after 32 minutes.
''If you play with 10 players, it is very difficult,'' Mancini said. ''But we started with a good attitude and pressed high as we wanted to win the game (and) it was easier after the sending-off.''
The visitors also ended the game with 10 men after captain Vincent Kompany was red-carded in the 75th for a wild two-footed challenge on Jack Wilshere, even though he got the ball.
City said it will make an appeal but if referee Mike Dean's decision is upheld and Kompany has to serve a three-match ban, Mancini will be deprived of another leading player with midfielder Yaya Toure at the African Nations Cup potentially until mid-February. Sergio Aguero is also out of action with a knee injury.
City's record at Arsenal was so bad that the champions had to go back to 1975 for their last league win at the home of the London club. They hadn't even scored a goal in their last five league visits to Emirates Stadium.
However, there was only going to be one winner once Koscielny was dismissed for wrestling Dzeko to the ground as they competed for a ball that had been flicked back into the penalty box.
''If it was a deliberate (foul), you cannot do that at this level, you cannot make mistakes at the back,'' said Arsenal manager Arsene Wenger, who felt his team was ''too timid'' in the early stages.
Koscielny's vehement protests toward Dean were in vain and although Szczesny saved Dzeko's penalty with his feet, with the ball rebounding off the post and back into the goalkeeper's arms, the respite was brief.
Milner, one of Mancini's go-to men in big games, rifled a fine finish in off the post in the 21st minute after being fed by Carlos Tevez's no-look pass, and then helped set up Dzeko's goal.
Tevez saw his flicked shot from Milner's low cross palmed away by Szczesny but only into the path of Dzeko, who tapped into an empty net for his 10th goal of the campaign.
Wilshere cleared Javi Garcia's header off the line in the final moments of the first half as City continued to press and it was more of the same in the second half until Kompany's red card for diving in two-footed toward Wilshere.
It gave Arsenal a fighting chance of salvaging something from the match - and substitute Olivier Giroud should have done better than heading a free kick over from eight yards out.
Joleon Lescott then cleared Theo Walcott's shot off the line as City held on.
A three-match ban would cause Kompany to miss Premier League games against Fulham and Queens Park Rangers as well as the FA Cup fourth-round match at Crystal Palace or Stoke.
Arsenal, meanwhile, stayed sixth - six points behind fourth-place Tottenham in the fight for a Champions League place. Arsenal has a game in hand, against West Ham on Jan. 23.
