Halftime report: 49ers 21, Browns 3

SANTA CLARA — Matt Breida’s 83-yard, lightning-quick touchdown run on the 49ers’ first snap sparked a fabulous start tonight against the Cleveland Browns.

The undefeated 49ers (3-0) took a 21-3 lead into halftime as they’ve dominated the Browns (2-2) on both sides of the ball.

Rookie Nick Bosa has led a defensive coming-out party that’s produced three turnovers and three sacks against Baker Mayfield and Co.

The 49ers have racked up 185 rushing yards, the final 19 of which came on Tevin Coleman’s first touchdown of the season for the 21-3 lead. Breida added a 5-yard touchdown catch to make it 14-0

On Breida’s 83-yard score, he was clocked at 22.3 mph, the fastest speed by a ball carrier this season, according to the NFL’s NextGen Stats.

The 49ers failed to convert either of the Browns’ first-quarter turnover into points, and kicker Robbie Gould has missed 47- and 52-yard field goal attempts.

Idle last week, the 49ers are vying for their first 4-0 start since 1990 as two-time defending Super Bowl champs.

Here are the studs and duds from first-half action:

STUDS

Matt Breida: His 83-yard touchdown run came once he raced through a massive lane, created by blocks from Kyle Juszczyk, George Kittle and Justin Skule. It was Breida’s first touchdown of the season, and his second promptly followed with a 5-yard touchdown catch on third-and-goal for a 14-0 lead.

Tevin Coleman: The season-opening starter returned from a 2 1/2-game absence (ankle sprain), and his 19-yard touchdown run pushed the 49ers lead to 21-3. A couple snaps before that, he converted a fourth-and-1 run into an 8-yard gain to the Browns 19.

Nick Bosa: His prime-time debut has been spectacular His pressure led to Sherman’s interception. He had a first-quarter fumble recovery. And he lined up next to Dee Ford on the right side as they bullied their way to a shared sack at the 6-yard line just before halftime. Then he capped the half by forcing Mayfield into an intentional-grounding penalty.

Starting secondary: Phenomenal half by every starting defensive back. Cornerback Richard Sherman, on the first play after Breida’s touchdown, made a midfield interception. Cornerback Emmanuel Moseley, making his starting debut, batted away a potential touchdown pass in the end zone. Nickel back K’Waun Williams made an interception at the 49ers’ 2-yard line (Antonio Callaway bobbled the ball). Free safety Jimmie Ward, starting in his season debut, made open-field tackles to twice stop Nick Chubb from scoring. And strong safety Jaquiski Tartt was solid in run support, combining with Nick Bosa to stop Chubb for a 5-yard loss in the red zone.

Kwon Alexander: One play after getting flattened on a blitz, he rebounded to share a third-down sack with K’Waun Williams at the Browns’ 6-yard line, forcing a punt on their third series.

George Kittle: From his Breida-springing block to an 18-yard carry of his own, Kittle relished the prime-time stage, as expected. He has two catches for 23 yards.

Bold calls: Kyle Shanahan successfully won a replay review on the game’s opening series, overturning a 31-yard, third-down conversion catch on the sideline by Ricky Seals-Jones against Richard Sherman’s coverage. Then, facing fourth-and-one from the Browns 27, Shanahan went for it, and Tevin Coleman converted with an 8-yard gain to the 19.

DUDS

Baker Mayfield: Last year’s No. 1 overall draft pick is 7-of-16 for 80 yards with two interceptions, three sacks, a lost fumble on a third-down strip sack and, in the final play before halftime, an intentional-grounding penalty with Bosa dragging him down.

Odell Beckham Jr.: Sure, he completed a 20-yard pass on the Browns’ first snap, but he followed with two drops, and his play-making ability was relatively contained.

Field-goal unit: Robbie Gould missed on 47- and 52-yard field goal attempts, and he’s 6-for-10 this season on a 49ers special-teams unit employing its third long snapper, Garrison Sanborn, whose lousy snap led to the 52-yard miss.

Deebo Samuel: The rookie failed to corral a third-down conversion pass on a crossing route, as cornerback Terrance Mitchell knocked the ball from his grasp. The 49ers were forced to punt after Sherman interception had that drive open at the Browns 41.

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