Mikel Arteta’s side were leading through Kai Havertz’s first-half strike when Rice saw red after the interval at the Emirates Stadium.
In a bizarre incident, the Arsenal midfielder earned a second booking for gently kicking the ball away and failing to retreat after fouling Brighton’s Joel Veltman.
Rice looked bewildered by the decision, while Arteta sought an explanation from the fourth official as Arsenal fans chanted “you’re not fit to referee” at Chris Kavanagh.
The Premier League said Rice was sent off for “delaying the restart”. VAR was unable to intervene because it was a yellow card and not a straight red.
Brighton took advantage of Rice’s dismissal to equalise through Joao Pedro, ending Arsenal’s 100 percent start to their bid to win the title for the first time since 2004.
The Gunners had won their opening two games of the season against Wolves and Aston Villa, but this was the first blow to their hopes of dethroning champions Manchester City.
Arsenal will be without the suspended Rice when they return to action after the international break with a north London derby trip to Tottenham on September 15.
“If it happens throughout the game in a consistent way it is fine but it didn’t. It is the inconsistency,” Arteta said of Rice’s red card.
“We started the game really well. We scored the goal, 1-0. We started the second half really good but then there is the decision that changes the game completely.”
Brighton boss Fabian Hurzeler inevitably saw it differently to Arteta, saying: “First of all he shoots the ball away so it is a clear yellow card, it changes the momentum of the game.”
