The Gunners were blitzed 5-1 at Anfield on Saturday - when they trailed 4-0 after just 20 minutes - and where later knocked off the top of the Barclays Premier League table by Chelsea, although Manchester City dropped points in a goalless draw at Norwich.
Wenger accepts his side did not produce the required performance of championship challengers, but is confident of a response against an inconsistent United side at the Emirates Stadium.
"It is always a disappointment to lose a game, but I think it was an accident because we have been very stable defensively and we have to treat it like that," said Wenger.
"We have just been on a 10-game unbeaten run. You cannot consider one game as the trend, the pattern of our season.
"It is an accident, not a welcome [one] of course, a very disappointing one, but a successful season is decided by how you respond to that.
"In any season you have disappointments, it is always down to the team to respond in a very positive way, that decides the success of the team."
Arsenal are set for a run of matches which could well define their season. Liverpool head back to north London for an FA Cup fifth-round tie on Saturday ahead of the visit of Bayern Munich in the Champions League on February 19.
Wenger intends to focus on the positives.
"We tend always to forget how good we are when we are not successful," he said.
"It is important that we remind them we have done until now very well, that we are in front of a very important week for us and we have worked very hard until now to be in that position."
Club-record signing Mesut Ozil produced another subdued display against Liverpool.
Wenger, though, has no issues with the contribution of the £42.5million German playmaker.
"He didn't have the best of games on Saturday, but that can happen. He works very hard to adapt to the physical level of the Premier League and for me he is an exceptional player," said Wenger, who should have France under-21 forward Yaya Sanogo available against Manchester United following five months out with a back problem.
"I wouldn't like to put too much pressure on him because he has been a top-class player until now.
"He knows when he is not good enough he will get questioned - that is normal."
Arsenal are asking fans to allow extra time for their journey to the stadium during the proposed industrial action by London Underground staff on Wednesday.
Wenger said: "The game will go on, that is for sure.
"We are sorry for our fans about the tube strike because many people will have to walk there, but we have improved the number of stewards and the safety and security of our fans should be guaranteed.
"Unfortunately it is not the best conditions to go into a game like that."