To be fair, the red card affects the game in their favour. I believe the result would be different if it's 11vs11 until the end. Not saying Manchester United won't be able to win, but it's not that hard to imagine Bilbao scores 1 goal or so.

That being said, Manchester United do have issues playing against team with 10 players or less in the past, so it's definitely good news that they managed to score 3 goals and dominate the game, especially on the second half.