SANTA CLARA, Calif. (AP) — Brock Purdy threw two touchdown passes and Christian McCaffrey ran for a score to lead the undefeated San Francisco 49ers to a 24-14 victory over the Denver Broncos on Sunday.

Both offenses struggled to generate offense on a hot day in the Bay Area, but the 49ers (4-0) took advantage of a fumbled punt return by Marvin Mims Jr. to set up a short touchdown drive in the third quarter that gave them the lead for good.

Purdy capped the 28-yard drive with a 1-yard touchdown pass to Deebo Samuel that made it 10-3 late in the third quarter. He then engineered a 74-yard drive that McCaffrey finished with a 1-yard run to extend the lead to 17-6 midway through the fourth after the Broncos (2-2) had settled for a field goal on fourth-and-2.

Bo Nix, who has thrived in late-game comeback situations, tried to mount another for Denver with his 13-yard touchdown pass to Jaylen Waddle cutting the Niners' lead to 17-14 with a 2-point conversion with 4:05 to play.

But Purdy sealed the win with a 56-yard touchdown pass to George Kittle with 2:15 to go. Purdy finished 19 of 30 for 218 yards and avoided taking a sack for a fourth straight game and committing no turnovers.

Nix struggled to push the ball downfield most of the game with Denver's running game unable to loosen up the defense. He finished 25 of 42 for 214 yards and one touchdown.

The 49ers came in scoring touchdowns on nearly half of their possessions, but struggled to move the ball against Denver's stout defense. They punted on two of their first three possessions with Purdy getting stopped on a fourth-down sneak on the other.

San Francisco got on the board with a 24-yard field goal to tie it late in the first half, but had a chance to take the lead thwarted when a field goal was blocked on the final play of the first half to keep the game tied at 3.

Broncos: CB Patrick Surtain (ankle), CB Riley Moss (ribs) and WR Pat Bryant (ankle) all left with injuries and didn't return.

49ers: FB Kyle Juszczyk left with a knee injury after being hit by Jahdae Barron and didn't return.

Broncos: Visit the Los Angeles Chargers next Sunday.

49ers: Visit Seattle next Sunday.

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