Harry Maguire admitted Manchester United conceded "two bad goals" in a dismal first half before fighting back to beat Atalanta.
Cristiano Ronaldo headed an 81st-minute winner at Old Trafford to send Ole Gunnar Solskjaer's side top of their Champions League group.
His late intervention came after Marcus Rashford and Maguire scored second-half goals to draw United level after they were stunned by their visitors.
United went into the game with Solskjaer under pressure, and his side were booed off at the break after Mario Pasalic and Merih Demiral gave Atalanta a shock 2-0 lead.
Maguire admitted the Red Devils had "made it difficult" for themselves with poor defending - but said he and his team-mates were confident they could turn it around in the second half.
"The first half we conceded two bad goals," the skipper told BT Sport. "We created a lot of chances in the first half so we knew that going into the second half.
"Yes, we made it difficult but we got there in the end.
"We know we’re working hard to be more solid and we got the result, that's what matters. We’ve conceded four in four from set pieces and we know that's not good enough."
After a poor opening period, United started the second half impressively, cutting the deficit thanks to Marcus Rashford's strike.
They struck the woodwork before Maguire levelled proceedings, slotting home at the back post with the poise of a seasoned striker.
He described his equaliser as "a proud moment", saying: "I’ve had a lot of chances this year but it’s my first goal for the season and in the Champions League.
"It’s a proud moment for me and my family."
And he reserved special praise for Ronaldo, who popped up with a crucial late winner having done the same against Villarreal before the international break.
"I was right behind Ronaldo," said Maguire his leap, his timing is always there, you see it all the time in training and he’s come up with the goods again."
Wins over Atalanta and Villarreal have got United's Champions League campaign back on track following a shock defeat to Young Boys in their group-stage opener.
While questions still being asked over their performances, United now top Group F at the halfway stage ahead of the return match in Bergamo in two weeks' time, before a trip to face Villarreal and a home match against Young Boys.Read More Read More