Mourinho added: "I told De Gea after the match, what I saw today was the best from a goalkeeper in the world".
Mourinho was then asked why he was not surprised, and said: "I can't answer to the second question".
There was controversy to be found, of course, with Arsenal having a pretty reasonable penalty shout denied in the game's later stages but perhaps the biggest scandal on the night was the sending off of United's Paul Pogba, who - as a result of his misdemeanour - will miss out on his side's crucial derby matchup with Manchester City next time around. "A bit disappointed with this colleague, Koscielny, with this kind of reaction", Mourinho said.
Danny Welbeck and Alexandre Lacazette, appealed in vain for penalties and, with his tongue firmly in his cheek, Mourinho said: "I know the pitch is wonderful and maybe breeds a desire to go to the floor".
But Arsenal are three points closer to the runaway Premier League leaders - and Wenger reckons this crushing defeat will just make his side even more determined to catch up.
In a post-match huddle which also included Jose Mourinho, Thierry Henry and William Gallas, he gestured that it may have been Bellerin's odd attempt to tackle that was to blame.
Jimbo Fisher leaves Florida State for Texas A&M
Longtime assistant coach and former Seminole All-American Odell Haggins will be the interim head coach. Fisher has spoken about his desire for Florida State to add its own football-only building.
"De Gea was man of the match by a clear mile", Arsenal manager Arsene Wenger said.
That said, Wenger was amazed they did not make more of the chances they created, especially once Paul Pogba was given a straight red card with 15 minutes remaining.
It was off a bad giveaway, and Arsenal had a second one moments later.
Antonio Valencia pounced on a Laurent Koscielny mistake to put United ahead after only four minutes, before Jesse Lingard finished a fine move involving Romelu Lukaku and Anthony Martial after forcing Shkodran Mustafi to concede possession.
"I felt that at the back our concentration was not sharp enough from the start and not dominant enough".
Arsenal's 33 shots were the most allowed by one of England's "Big Five" clubs in last seven seasons, but they had only Alexandre Lacazette's goal to show for their efforts thanks to De Gea's brilliance. We were not decisive enough.