The Gunners were blitzed 5-1 at Anfield on Saturday - finding themselves 4-0 down after just 20 minutes - and were later deposed at the top of the Barclays Premier League table by Chelsea.
Wenger, though, insists headlines revelling in the downfall of his side are somewhat premature given their other results in what has generally been a promising campaign.
"We tend always to forget how good we are when we are not successful," said Wenger, who should have France Under-21 forward Yaya Sanogo available against United following five months out with a back problem.
"It is important that we remind them we have done very well until now, that we are at the start of a very important week for us and we have worked very hard until now to be in that position.
"Let's also not forget that we have put in some convincing performances as well - against Tottenham (in the FA Cup), Liverpool (at home in the league), at home to Napoli and in Dortmund (in the Champions League).
"We can show now until the end of the season that people who think (we cannot win big games) are wrong."
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 Sunday ahead of the visit of Bayern Munich in the Champions League the following Wednesday.
Wenger intends to focus on the positives.
He said: "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.
"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."
Club-record signing Mesut Ozil produced another subdued display against Liverpool.
Wenger, though, has no issues with the contribution of the German playmaker - who arrived from Real Madrid in a much-hyped £42.5million deal on deadline day in September but whose last eight appearances have returned only two assists and no goals.
"Ozil 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.
"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."
With the cancellation of a proposed strike on the London Underground on Wednesday, Arsenal will be able to prepare as normal to get their own staff to the Emirates Stadium along with an expected capacity 60,000 crowd.
While United may not be the force they were last season following Sir Alex Ferguson's retirement, Wenger will not take the challenge of David Moyes' men lightly.
"We consider them as a strong side and a team that of course has quality," he said.
"Their season is difficult to judge at the moment. We will be playing against a good team and we want to beat them."
Wenger, meanwhile, refused to be drawn on rumours Arsenal were ready to launch a £15million summer bid to bring United forward Robin van Persie back to north London.
"I don't think that is an ideal subject for us to treat today," he said.