"Lukaku's goalscoring record is up there, it's fantastic, he scores goals", he added.
United now face away games against Juventus in the Champions League and Manchester City in the Premier League and if they repeat this lacklustre performance, they are unlikely to escape with anything less than two heavy defeats.
But Mourinho claimed his side's open back line is a symptom of a more aggressive style of play compared to the tactics he used in last term's second-placed Premier League finish.
Former Manchester United midfielder Quinton Fortune has stressed that Jose Mourinho's side can not keep underperforming in the first halves of games and hope to get away with it every time.
"The approach [last season] was much more defensive and with a much more defensive approach you can hide better your weaknesses", Mourinho said.
He added that he was frustrated by the team continuing to start slowly, "I really can not understand the kind of [early-match] mentality that brings me more white hair!"
"When we make a defensive mistake, instead of forgetting and keeping playing, it is something that triggers instability". People watching this game will not believe how hard we worked this week.
United built on this and improved significantly in the second half, but failed to find the goal to put them ahead until stoppage time when Rashford controlled a Paul Pogba cross and smashed home from close range at the second attempt. When we are in control we have no problems, when the opponent is in control I think the team has problems. We passed the ball well and there was really good intensity to our play.
"It's a tough one for us", he said. I think [he] was the impact in the team. We knew the second half was going to be a different game. At half time, I thought I was the luckiest manager in the Premier League, to be at 1-1 in a half in which it should be 5-2 or 6-2 [to Bournemouth].