FOXBOROUGH, Mass. — The New England Patriots had a commanding lead. Then they had their worst quarter of the season.

So Coach Bill Belichick, occasionally perky after victories, was his more recognizable dour self Monday after subjecting himself to another look at the fourth-quarter flop against the winless Indianapolis Colts.

“Couldn’t make a first down in the fourth quarter, couldn’t keep them out of the end zone in the fourth quarter,” he said one day after the Patriots’ 31-24 win. “They just did a better job than we did.”

Much better.

The Patriots entered the final period with a 31-3 lead, hardly surprising since they were three-touchdown favorites. But the last quarter was a nonstop nightmare. Their defense allowed 266 yards and 16 first downs. Their offense gained just 11 yards and managed no first downs. If Deion Branch hadn’t recovered an onside kick with 36 seconds left, it might have been even worse.

“That wasn’t the way we wanted to finish the game,” Branch said, “on either side of the ball.”

Still, the Patriots (9-3) won their fourth straight game and remained tied for the best record in the AFC. They have another weak opponent next Sunday when they visit the Washington Redskins (4-8), who have lost seven of their last eight games.

But after holding on to beat a team that fell to 0-12, the Patriots aren’t about to take anything for granted.

“It’s disappointing. Go back to the drawing board and try to improve,” linebacker Jerod Mayo said. “We just have to learn how to put two halves together next week.”

The Patriots began the game with a curious defensive lineup, a result of injuries to some players and poor play by others.

Nate Jones, signed a few days earlier, and Matthew Slater, a wide receiver, started at safety. Niko Koutouvides, primarily a special teams player in his other seven NFL seasons, notched his first start at linebacker for New England after being signed Nov. 9.

All played fairly well, with Jones posting nine tackles, second most on the team. Slater had seven and forced a fumble. Koutouvides posted six.

“I thought Nate did a good job,” Belichick said. “He wasn’t even familiar with what we were doing, so he had a steeper learning curve. … It was far from perfect, but I thought he did a good job.”

Slater played some defense early in his career but didn’t have much time to prepare for Sunday’s assignment.

“I think he did all right,” Belichick said. “He made a few plays, made some tackles, caused a fumble. There were certainly things he could have done better as well. … He really hadn’t had a lot of practice time back there either, to be honest with you, this year, although he’s done it in the past.”

Koutouvides said communication can be difficult among players who haven’t been on the field together much.

“But you can’t make any excuses,” he said. “Whoever is out there on the field has to play (at) a high level. I know that at the end of the game we didn’t finish in the right way, so we need to change that.”

In his first start of the year for the Colts, Dan Orlovsky completed 18 of 20 passes for 240 yards and two touchdowns in the fourth quarter alone. The Colts scored on a 5-yard run by Donald Brown with 10:24 to go and passes to Pierre Garcon of 33 yards with 2:12 left and 12 yards with 36 seconds remaining.

On that final touchdown and the 40-yard completion to Garcon on the previous play, cornerback Devin McCourty, a Pro Bowl player as a rookie last year, covered the receiver.

“We’ve got to finish games,” safety James Ihedigbo said. “Against other teams, it won’t be good enough.”