Manchester United defender Chris Smalling reveals manager Louis van Gaal told the side they had been "unacceptable" during his half-time team talk.
The Red Devils struggled to cope with Burnley's pressure in the first 45 minutes of the game and were lucky to be in front after the 25-year-old scored both goals for his team.
And the Englishman believes that the hard-fought win shows that there is room for improvement ahead of the last part of the season.
"It wasn't a 3-1 scoreline game," Smalling told MUTV.
"Especially in that first half, we all let ourselves down. We could have played much better.
"There is [more to come]. But the manager said in the dressing room that the first half was unacceptable and all the players know that.
"If we can win games playing that badly, then it shows that if we do play well and it all clicks, then there will be a lot better performances at Old Trafford, that's for sure.
"They [Burnley] came out of the traps, they pressed us well, but we didn't find the solutions to that in the first half.
"We were very lucky to come in at half-time ahead. We knew that Burnley run hard and run the channels. We knew their game-plan but we didn't get to grips with it.
"It was pretty unreal [scoring after 22 seconds], it was quite fortunate because when you come on as a defender, it's never easy but, if you've got a corner, it puts you on the front foot straightaway and luckily I got free.
"[The goal] helped settle us a little bit going into the second half. That second half was a little bit more like Manchester United. But that first half - we need to look at ourselves and make sure it never happens again."
