Michael Carrick accepted Manchester United made far too many mistakes on a "bad day" as they suffered their heaviest defeat of the season at Arsenal.
United, who began the weekend as Premier League leaders, were beaten 3-0 at Emirates Stadium after going two goals behind inside seven minutes.
Vice-captain Carrick rued their wretched start and admitted he and his teammates did not close Arsenal down well enough.
"We just didn't start well enough, or quick enough, and conceded goals," he told MUTV. "When you concede goals at this level then it makes it difficult to come back. I think we improved as the game went on, but it just wasn't good enough from us.
"It was certainly a bad day. We just gave them a bit too much space and they played well and it came off for them.
"We did too many things wrong; you could go on forever talking about why things didn't work, but we just didn't start well enough, conceded the goals and gave ourselves too much to do."
United face a demanding October, with Everton and Manchester City their next opponents in the Premier League, and Carrick is vowing that they will respond.
"We are bitterly disappointed and will probably beat ourselves up about it over the next few weeks, but we'll come back looking at the bigger picture," he added.
"It's a setback, but we're still up there and just need to take this one on the chin, take whatever criticism comes our way and come back stronger."