Erik Ten Hag’s side had started the game well, but fell behind in the 28th minute when Leroy Sané’s tame effort from outside of the box was palmed in by the United goalkeeper.
The drawback deflated the away side, who quickly conceded a second when Jamal Musiala’s brilliant play led to him teeing up Serge Gnabry to cooly slot home.
“It’s difficult. We started very good. After my mistake we lost control of the game,” Onana told TNT Sports following the match.
“The team were one down because of that mistake. I have to learn from it and be strong. I’m happy with the comeback of the team.
“I have a lot to prove. My start in Manchester hasn’t been so good, not how I want. This was one of my worst games. We have big ambitions.
“It’s a tough time. We have to be together and work hard.”
Manchester United did manage to provide themselves with a lifeline however, with Casemiro’s two late goals meaning The Red Devils can head to Old Trafford only losing by a single goal.
Onana hasn’t enjoyed the best of starts since moving to the Premier League side in the summer, the David De Gea replacement also being criticised for his attempt to stop Nottingham Forest’s opener a few weeks ago.
Only two sides in the division have conceded more goals than United, who are currently in the midst of an injury crisis in the defence department.
Analysing the match for TNT Sports, former Manchester United defender Rio Ferdinand said he appreciated Onana’s frank post-match interview, but criticised the goalkeepers overall performance.
“I respect that,” Ferdinand said. I’ve lost games and made mistakes and refused to speak to the media at times. That showed good character and showed he’s made of the right stuff.
“He’s as confident as you like with his feet, but as a goalkeeper, you’re paid to come in and make saves.
“He should save it, it is meat and drink for him. He should be picking this up and looking for his next pass. It’s a very, very bad mistake and one that he needs to recover from.”
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