Provo • The third quarter was not the charm for the BYU Cougars late Saturday night.

And neither was the fourth.

California dominated the second half — a week after the Cougars used the period after halftime to beat Arizona — and took a 21-18 win over punchless BYU at LaVell Edwards Stadium.

Cal’s defense completely shut down BYU’s offense in the second half, allowing just 21 yards until BYU’s final drive.

“We didn’t do enough to win this game,” BYU coach Kalani Sitake said. “Effort is not enough to win games. We need to be more efficient as an offense and more disruptive as a defense.”

The Cougars went 73 yards in 13 plays to get within three points with 51 seconds remaining, but an onside kick was not successful and Cal rode off with its second win. BYU dropped to 1-1.

Until the final drive, It was eerily reminiscent of 2017, when BYU had one of the worst offenses in college football. Nothing worked in the second half until the late drive.

After completing 12 of 22 passes for 108 yards in the first half, BYU quarterback Tanner Mangum was mostly shut down after the break and finished with 196 passing yards. Seventy-six of those came on the final drive. He was intercepted twice.

“It’s got to get better,” Sitake said of Mangum’s performance. “Dropping the ball [by receivers] doesn’t help, either.”

Cal pushed its 7-3 halftime lead to 14-3 early in the third quarter when Noa Kanawai broke free on a delayed wheel route and caught an easy 52-yard touchdown pass from Chase Garbers.

BYU safety Dayan Ghanwoloku blew the coverage on the Cal TD pass, but he made amends moments later. Butch Pau’u separated Cal’s Derrick Clark from the football, and Ghanwoloku returned the fumble 36 yards for a score.

“We can’t give up layups,” Sitake said of Cal’s touchdown. “We can’t give up free points.”

The Cougars’ defense came up with another big play on Cal’s next possession, as redshirt freshman Isaiah Kaufusi returned an interception 20 yards to the BYU 43. But three plays netted just 5 yards, and the Cougars had to punt for the fifth time.

“The effort was there, the heart was there, and we finally figured it out late,” said tight end Moroni Laulu-Pututau. “But you can’t do that against a team as good as Cal.”

The Bears wouldn’t give it away on their next possession. They drove 85 yards in 11 plays and took a 21-10 lead with 13:42 remaining on quarterback Brand McIlwain’s 2-yard touchdown run.

Ghanwoloku jumped on a muffed punt early in the fourth quarter to put BYU in business at the Cal 16, but Mangum was intercepted on third-and-long by Travion Beck. It was that kind of night for the BYU offense until the Cougars took over with 3:38 remaining and capped the drive with a 1-yard touchdown pass to Brayden El-Bakri.

“Lack of communication,” was El-Bakri’s explanation for the offense’s woes.

The Cougars moved the ball well in the first half, but managed just a field goal thanks to some dropped passes and failed fourth-down attempts. Cal had 124 yards in the first half, 80 on one drive that resulted in a 25-yard touchdown pass. The Bears finished with 387 yards, 214 passing and 173 rushing.

BYU had three drives of 10 or more plays in the first half. The Cougars had the ball for nearly 20 minutes — and Cal for just more than 10 minutes — but Mangum’s 12 completions went for just 108 yards.

“We didn’t help ourselves by making some errors and some drive-killing mistakes,” Sitake said.

The Cougars picked up 79 yards on their first two drives, but Cal slowly figured out how to stop BYU’s running plays, and Mangum couldn’t beat it deep. Beau Hoge was stopped inches short on a fourth-and-1 gamble at the Cal 33 on BYU’s first possession.

Sitake explained going for it on fourth down twice in the first half, rather than to attempt long field goals, by saying he thought the Cougars were winning the line of scrimmage.

“We will get it fixed,” Sitake said.

Cal went three and out on its first series, then put together an 11 play, 80-yard touchdown drive the second time it had the ball. The drive was kept alive when Vic Wharton III came up with a 12-yard catch on fourth-and-5, and ended with Patrick Laird’s 25-yard touchdown reception.

The Cougars moved the ball well on their third possession, but the drive stalled at the Cal 19 and freshman Skyler Southam kicked his first career field goal, a 36-yarder.

A pair of dropped passes by Dylan Collie and Micah Simon cost the Cougars dearly late in the first half. Collie lost the chance for at least a 40-yard catch with the drop and Simon’s drop came on third-and-5 and halted a promising drive because Mangum was sacked on the next play when BYU coaches went for the first down instead of what would have been a 52-yard field goal attempt.