FOXBOROUGH, Mass. -- Seemingly set to sack Tom Brady in the fourth quarter and perhaps turn the game in favor of the Kansas City Chiefs, rookie linebacker Breeland Speaks inexplicably set him free.

Brady instead scored New England's go-ahead touchdown and the Chiefs' final lead in what would be a 43-40 defeat was gone. Speaks later said he turned Brady loose because he thought he had already thrown a pass and didn't want to risk a roughing the passer penalty.

"We're in New England," Speaks said. "Tom Brady's going to get the call. We were already down there. I didn't want to put us on the inch-yard line."

It was a learning moment for Speaks, a second-round draft pick who was making the first start of his pro career in place of the injured Justin Houston. Speaks wasn't the only player with some things to atone for after another bad outing for the Kansas City defense.

Speaks and his defensive teammates need to learn from and atone for their mistakes quickly. Otherwise, the Chiefs' defense will ruin a potentially good thing.

The Chiefs forced the Patriots into one turnover, when Speaks stripped the ball from Brady on an earlier play. They stopped the Patriots once on downs early in the game.

Otherwise, New England scored on its other nine drives, not counting a one-play possession at the end of the first half when the Patriots were content to kill the clock. The Patriots didn't punt all night.

"When you score 40 points and you lose, you've got to look at yourself in the mirror," cornerback Orlando Scandrick said.

Introspection is a good thing, but playmaking is even better. Other than Speaks' strip-sack of Brady and teammate Allen Bailey's recovery, that was in short supply against the Patriots. The Chiefs forced five turnovers in their previous game against Jacksonville but found Brady and his receivers and backs far more difficult to deal with.

The Chiefs played without Houston, perhaps their best all-around defender. They were also missing another injured edge rusher, Tanoh Kpassagnon, and four of their top safeties, also because of injuries.

That forced the Chiefs to turn to some largely untested players. Safety Josh Shaw was one. Playing in his first game with the Chiefs, Shaw was beaten by tight end Rob Gronkowski on a 39-yard pass that set up New England's winning field goal.

Speaks was another. He had a sack, the first of his career, and was in one five other tackles.

It wasn't good enough to help the Chiefs win. His play has to be better next week against the Cincinnati Bengals at Arrowhead Stadium, assuming Houston's injured hamstring keeps him out again.

"You're not going to succeed as much as you want to in the beginning but you need those experiences to learn," said linebacker Dee Ford, who had his own struggles early in his career as a first-round draft pick. "One real-life encounter is worth a thousand observations. Experience is your best teacher. He's going to move on. He's going to move forward."