Tom Brady and Bill Belichick accepted the New England Patriots' performance against the Baltimore Ravens was not worthy of victory after they fell to their first loss of the season on Sunday.

The Patriots had glided through the first eight games of their schedule as they remained unbeaten through the opening half of the campaign, but they came unstuck at M&T Bank Stadium in a 37-20 defeat.

New England's loss drops them to 8-1 and leaves the San Francisco 49ers (8-0) as the NFL's last remaining unbeaten team.

Brady and the Patriots offense endured a particularly difficult evening in Baltimore as New England turned the ball over twice and committed uncharacteristic penalties in a performance that will give hope to their AFC rivals in the race to the Super Bowl.

"Losses always find a way to recalibrate how you see yourself. And we obviously have a lot of work to do," said Brady.

"So just wasn't obviously good enough. Get beat by 17 points, that's not what we're all about. I give the Ravens credit. I think they played really well, took advantage of their opportunities. And that's what it takes."

Head coach Belichick agreed with his quarterback's assessment.

"We've all got to do a better job. That includes everybody -- period," Belichick said. "We competed out there, but it just wasn't good enough. We all have to do a better job, starting with me.

"We didn't do anything well enough to deserve to win."