A Niners’ knockout

SANTA CLARA, Calif. — Brock Purdy threw three of his four touchdown passes to George Kittle and the San Francisco 49ers extended their dominance over the Dallas Cowboys with a 42-10 victory Sunday night.

The Niners (5-0) knocked the Cowboys out of the playoffs in tight games the past two seasons, adding intrigue to this early season matchup between perceived contenders.

The rematch wasn’t even close.

The Niners led 14-0 before the Cowboys got their initial first down of the night and were never really threatened on the way to matching a franchise record with their 15th straight regular-season win and earning their fifth 5-0 start.

Purdy calmly picked apart the league’s stingiest defense to improve to 10-0 as a starter in the NFL and San Francisco’s defense made life difficult on Dak Prescott all night.

“The defense does their job, so it makes life easy for me,” Purdy said.

Prescott was sacked three times and heaved an interception into double coverage after Dallas fell behind 28-10 in the third quarter. He threw two more interceptions in the fourth quarter with his only highlight coming on a 26-yard TD pass to KaVontae Turpin in the second quarter.

“It was such a great night for the whole defense, the whole team,” said linebacker Fred Warner, who had a sack, an interception and a forced fumble. “It was so fun out here today.”

It was Dallas’ most lopsided defeat since losing 49-17 to New Orleans in 2013.

Purdy again was nearly mistake free. A week after throwing only one incomplete pass in a win over Arizona, he repeatedly found openings downfield to Brandon Aiyuk, Deebo Samuel and especially Kittle.

Purdy finished 17 for 24 for 252 yards and has not thrown an interception all season. He connected on a 19-yard TD pass to Kittle on the opening drive, a 38-yarder early in the second quarter on a reverse flea-flicker and then a 10-yarder to put the game away in the third quarter.

  Gallery: Dallas Cowboys at San Francisco 49ers  

Kittle became the first Niners player with three TD catches in a game since Vernon Davis in 2009.

Purdy added a 1-yard TD pass to Kyle Juszczyk in the fourth quarter.

The Niners took the opening kick and drove 75 yards in seven plays to score on a 19-yard pass from Purdy to Kittle to take the lead. San Francisco has four TDs and one field goal on the opening drive this season for a league-leading 31 points.

The 49ers were just as tough on defense early, holding Dallas to 6 yards in the first quarter and no first downs for more than 17 minutes.

McCaffrey scored on a 1-yard run in the second quarter after losing a fumble near the goal line earlier in the game. It was the 14th consecutive game he has scored a TD in the regular season or playoffs. The only players with longer streaks are Lenny Moore (17 games), O.J. Simpson (15) and John Riggins (15).