England boss Eddie Jones said his team were "not good enough" and captain Owen Farrell raised discipline worries after a surprising 30-29 defeat to Argentina at Twickenham.
In front of an 80,000 full house, the home side were edged out by the Pumas, getting their Autumn Nations Series campaign off to a rocky start.
Head coach Jones said England were left "chasing our tail" after letting a half-time lead slip away.
"We made silly mistakes, but I like the way the team went about it. We didn't finish well, there was that lack of cohesion," Jones said on Amazon Prime Video.
"It's not good enough – we realise it's not good enough. We kept making fundamental mistakes."
As Argentina celebrated a first win against England since 2009 and a first at Twickenham since 2006, the defeated hosts set about working out what went wrong.
They allowed Emiliano Boffelli and Santiago Carreras to cross for second-half tries, with Boffelli finishing with 25 points in all thanks to his strong kicking performance.
Farrell said England must show a response, with matches against Japan, New Zealand and South Africa to come this month.
"We've got a long way to go this autumn and need to make sure we don't drop any confidence because of this," Farrell said.
On a boggy surface, England failed to cope as well as their visitors, and Farrell said: "We kind of let the pressure off a lot of the times. We played the game we thought we needed. It's a wet, wet pitch and both teams didn't really move the ball that well.
"We weren't at our best, definitely not, and that's what were here to do, to get the best out of ourselves.
"We'll have a good look. There were some good bits, and it felt like it was coming. I just think a bit of discipline and errors of not quite being on the same page at times cost us that extra bit of momentum, what it takes to get in front and stay in front."
Boffelli said Michael Cheika's victorious team would enjoy their big moment.
He said: "I'm very happy, we are very happy. Tomorrow we will think about Wales, that follows. We spoke about how we must try to stay close in the score."
Speaking about the influence of Australian coach Cheika, who guided Argentina to wins over Australia and New Zealand in this year's Rugby Championship, Boffelli said: "Everyone knows Michael Cheika as a coach, and it's very important for us.
"He has experience in international rugby and he is confident in us, and that's good. I'm very happy with that, but the team did a good day."