Little-known BenJarvus Green-Ellis gave the Patriots a boost in the tight AFC East race.

And he helped hand the free-falling Buffalo Bills a costly loss.

The undrafted rookie from Mississippi rushed for a career-high 105 yards and scored a touchdown for the fourth straight game and New England’s defense dominated in the second half for a 20-10 win on Sunday.

Green-Ellis began the season on the practice squad but is the Patriots’ top runner with Laurence Maroney on injured reserve and Sammy Morris missing the last three games and LaMont Jordan out for the last five.

“Wherever we are on the field, I just try to get it to the end zone,” Green-Ellis said. “That’s my job every play.”

He capped a 19-play drive with a 1-yard touchdown with 1:57 left long after Matt Cassel rushed for a 13-yard touchdown on the Patriots’ first series. Cassel, the steadily improving replacement for Tom Brady, directed the offense with poise and completed 23 of 34 passes for 234 yards.

The defense held the Bills to 58 yards in the second half—while the offense piled up 192. The Patriots had the only two interceptions of the game and outgained the Bills 370-168.

“When you don’t allow big plays, it definitely keeps control of the game in your favor,” cornerback Ellis Hobbs said.

The Patriots (6-3) moved a game ahead of the Bills (5-4), who are 1-4 since winning their first four games. The New York Jets routed St. Louis 47-3 and remained tied with New England. Miami (5-4) beat Seattle.

“We realized this was a big pivotal game,” Bills linebacker Paul Posluszny said. “We have to get a winning feeling and we don’t have that now.”

The loss—Buffalo’s 10th straight to New England—was especially harmful since the Bills had lost their previous two games against the Dolphins and Jets and dropped to 0-3 in division games. The Patriots are 2-1 against AFC East opponents and face the Jets and Dolphins in their next two games.

“It’s getting down to crunch time now,” Patriots linebacker Tedy Bruschi said.

After Green-Ellis’ score capped a 19-play drive, the Bills got their only touchdown on a 14-yard pass from Trent Edwards to James Hardy after an 85-yard kickoff return by Leodis McKelvin.

That was hardly enough against a strong defense.