FOXBOROUGH, Mass. (AP) — Tom Brady limped off the field under the worried stares of Patriots fans. The thing they feared most finally happened — losing the NFL's reigning MVP to injury.

And the team they love more than any other plummeted from an exclamation point of an unbeaten 2007 regular season to a huge question mark in 2008 after it held on to beat the Kansas City Chiefs 17-10 Sunday.

Brady hurt his left knee when tackled by safety Bernard Pollard midway through the first quarter. He went to the locker room and didn't return. Matt Cassel, who had thrown only 39 passes as Brady's backup the past three seasons, took over.