The 87th-minute dismissal marked Chelsea's fifth red card in six games across all competitions.
Despite the growing count, Maresca insists he's not worried.
"It's something we can do better, but I'm not concerned," he said post-match. "Yes, we can avoid it, especially at 3-0 when the game is finished. But I also value the desire to not concede. Malo [Gusto] made a mistake, but it shows he cares."
Goals from Josh Acheampong, Pedro Neto, and Reece James sealed a comfortable win for Chelsea, lifting them to eighth in the table. However, the first-half performance was shaky, with Forest dominating possession and Chelsea looking sloppy on the ball.
Maresca, watching from the stands due to a touchline ban, admitted the team struggled in possession:
"Off the ball, we were good. On the ball, not good enough. We gave the ball away too much, looked sloppy in build-up."
Still, he praised the players' attitude and second-half improvement.
"They were shouting in the final minutes, 'don't concede.' That desire is important. The red card can be avoided, but the mindset is something I like."
With discipline becoming a pattern, Maresca stressed balance: reducing mistakes without losing the intensity that drives strong defensive efforts.
Manchester City secured a second successive Premier League victory at home against Sunderland, Chelsea were held scoreless away to Bournemouth while Tottenham managed to beat Brentford.
Enzo Maresca has admitted Chelsea are still unsure when Romeo Lavia will return, as the Belgian's injury problems continued to disrupt their midfield plans ahead of Saturday's trip to Bournemouth.
Enzo Maresca admitted that Cole Palmer's long-awaited return was "the only good news" on a punishing Wednesday night for Chelsea, who were beaten 3-1 by a sharp Leeds United side at Elland Road.
Leeds United hauled themselves out of the relegation zone with an energised 3-1 victory over Chelsea on Wednesday, a result that relieved growing pressure on manager Daniel Farke.
