Mikel Arteta proud as Arsenal salvage point from 'impossible' position
Arsenal have finished second to City in each of the past two seasons and were seconds away from landing a massive early psychological blow in the title race until John Stones levelled in the 98th minute.
Erling Haaland's 100th City goal had fired Pep Guardiola's men into an early lead.
But Arsenal wrestled control away from the English champions thanks to goals from defenders Riccardo Calafiori and Gabriel Magalhaes.
Trossard was then shown a second yellow card on the stroke of half-time for kicking the ball away after committing a foul.
Arteta was furious after Declan Rice saw red in similar circumstances in a 1-1 draw against Brighton last month.
"We were thrown into a context of the game that makes it almost impossible for 56 minutes," said Arteta.
"I'm so proud of them. You cannot be thrown in a more difficult situation and the way we handled the situation is unbelievable."
Arteta responded by sacrificing Bukayo Saka for an extra defender in Ben White at half-time as the visitors packed their penalty box to deny City any space to breakthrough.
Guardiola's men seemed set for a first home defeat in all competitions since November 2022 until Stones bundled in from a corner at the death.
Arteta added: "99 out of 100 times you play 56 mins in this stadium 10 against 11 you are going to lose and lose by a lot of goals.
"It's unbelievable how they react but I cannot be happy because I want to be in a situation where we can enjoy the game."
A draw leaves Arsenal still two points behind leaders City.
But they have largely minimised the damage from being handed tough trips to Aston Villa, Tottenham and their title rivals inside the first five league games of the season.
"The boys put so much into every single action," said Arteta. "They have made another big step today as a team and individuals."
Guardiola hailed Arsenal's physical and mental resilience to hold out for so long.
"Congratulations to Arsenal. To be so strong mentality blocking for long, long minutes but we were so patient to do it," said Guardiola.
"This is one of the best teams in the world - Arsenal. In many things they are really good."