Callum Hudson-Odoi believes he and his Chelsea team-mates let themselves down as they lost their Boxing Day London derby to struggling Arsenal.
The Gunners had not won a Premier League game since November 1 but ran out deserved 3-1 winners.
An Alexandre Lacazette penalty, Granit Xhaka free-kick and Bukayo Saka cross-cum-shot had Arsenal coasting – with Tammy Abraham grabbing a late consolation and Jorginho then missing an injury-time spot-kick of his own.
While victory was hailed as a potential "turning point" by Arsenal boss Mikel Arteta, his Chelsea counterpart Frank Lampard has now seen his Blues lose their third away league game in a row.
Hudson-Odoi came off the bench with Jorginho at the interval and helped add a spark to Chelsea's misfiring forward line.
But the England international admits it was not good enough from the team after Lampard had criticised them for a poor first-half performance.
"It feels like we let ourselves down," he told the official Chelsea website.
"We know that we can do much better than we did. We should have put the same energy we had in the second half into the first half as well.
"We should have had the same attitude from the get-go and pushed all the way through the 90 minutes. So we're really disappointed in ourselves.
'We started too slow, we all know that. We knew from the start it was going to be a difficult game no matter what. They're Arsenal, they're a good team.
"We wanted to come out here and try and get the three points but unfortunately we didn't."
It is a quick turnaround for Chelsea as they look to get another defeat out of their system – but it is a visit of high-flying Aston Villa next on Monday.
"We've got to reflect on ourselves between now and Monday and hopefully we'll bounce back in that game," added Hudson-Odoi.
"We know we could have done better in every aspect, but we've got to go back to the training ground and try to work on everything we did wrong."
Arsenal, meanwhile, will be keen to keep the momentum of an important win when they travel to face Brighton on Tuesday.
"It's a really important week for us," said Arteta.
"Some of the performances haven't been enough to win football matches and that is something difficult to handle over time.
"That confidence that we can come away from games with the points and the boys are delighted and I am really happy for them and of course for our fans, because there have been some difficult weeks."