The 49ers suffered another collapse in the fourth quarter under coach Kyle Shanahan

SANTA CLARA, Calif. (AP) — The defense withered in the heat, the offense couldn't finish drives or protect the ball and the San Francisco 49ers frustratingly squandered another late lead to a division opponent.

Brock Purdy threw two interceptions in the second half, Jordan Mason lost a fumble in the red zone and San Francisco allowed Kyler Murray and the Arizona Cardinals to score two points in the fourth quarter 24:23 defeat Sunday seemed eerily familiar to me, like a previous loss to an NFC West opponent.

Two weeks after blowing a 24-14 fourth-quarter lead against the Los Angeles Rams, the Niners (2-3) did it again as they failed to defend their 23-13 lead against Arizona. This was the sixth time they blew a double-digit lead in the fourth quarter of the regular season and playoffs under coach Kyle Shanahan, which is the most of any coach in the NFL since he was hired in 2017.

“It’s super frustrating,” All-Pro left tackle Trent Williams said. “Obviously we have to figure out how to finish games and how to get teams out early when we have the chance.”

The Niners had plenty of chances to stay in control thanks to a blocked field goal that Deommodore Lenoir returned for a touchdown in the first half and a Nick Bosa interception that set up a field goal.

But San Francisco left the Cardinals hanging in the game and came out late when Murray threw a 2-yard TD pass to Elijah Higgins, followed by James Conner's 2-point conversion that made it 23-21.

Murray then, under heavy pressure, converted a fourth-and-5 pass to rookie Marvin Harrison Jr. on the winning drive while the running game did the rest.

“We kind of melted down in the second half,” All-Pro linebacker Fred Warner said. “Too many leaks, missed tackles, not the right fit.”

The offense's mistakes were even more costly. The 49ers settled for field goals three times after getting inside the 10 in the first half. In the second half, they had another drive in the red zone and ended with a turnover on downs when they attempted 4th-and-23 because kicker Jake Moody was out with a high ankle sprain.

Then came the most costly mistake, when Jordan Mason lost a fumble on first-and-goal with 6:20 to play in the 8th minute and San Francisco defended a two-point lead.

“I just have to be better and more aggressive down there, and once we get down there, obviously we all have to have the mindset as a unit that we have to push through this,” Purdy said. “We know we can settle for a field goal, but we have to hold ourselves to a higher standard and cross the goal line.”

Despite all of that, the 49ers still had a chance when they took over at their own 27 with 1:32 to play. Purdy completed a 15-yard pass to George Kittle to get the drive going. But on the next play, Jalen Thompson got free on a blitz and hit Purdy, forcing a floater that was intercepted by Kyzir White to seal the win.

After going 11-1 in the division over the last two seasons – the only loss coming when several starters were rested in a Week 18 game against the Rams last season – San Francisco has its first two NFC Lost West games and is on the verge of a showdown with the first division team. Place Seattle on Thursday evening.

“The standard here is excellence,” Purdy said. “What we have proven in recent years is what we want to achieve. It's still early in the season and we're still trying to find our true identity as a team. We're getting there. It's just a few more games and a few rides before it gels and sticks together. That's why I'm confident we'll find it.

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