Wenger had a winning record against Fergusson until the CL semi-final in 2009. He came to Arsenal in 1996. Not too bad against the best manager ever arguably and also someone who spent way more than Wenger on building those teams. One only has to see our team sheets for matches against United post that loss to assess why that record was overturned.
Tottenham didn't beat us in the League for over 12 seasons straight, not a bad North London derby record, in fact an enviable derby record full stop. That, for a mentally weak manager who sends out under prepared teams.
Our loss to Chelsea in the CL in 2004 was our first loss to them under Wenger too.
However, we really should have beaten United this season.