SANTA CLARA, Calif. -- Late in the first quarter of Sunday's win against the Arizona Cardinals, the San Francisco 49ers faced a third-and-4 at Arizona's 39-yard line. Niners coach Kyle Shanahan called for a handoff to running back Christian McCaffrey, the type of call you make when you are already planning to go for it on fourth down.

After the Cardinals stopped McCaffrey for no gain, Shanahan wasted no time sending the fourth-down play to quarterback Brock Purdy. It was a pass, one Purdy squeezed into well-covered tight end George Kittle for a 9-yard gain and a first down on the way to San Francisco's second touchdown in its 35-16 victory.

More than those outcomes, the call was the latest example of Shanahan's implicit trust in Purdy, which the second-year quarterback has earned since taking over the starting job in Week 13 of last season.

"He's [been] extremely consistent in practice since he's been here and he's been the same in games," Shanahan said. "What you guys see is what we see and it's what we feel."

As the quarterback of the 49ers' juggernaut, Purdy is a constant target for critiques and nitpicking. The nonbelievers say he's simply a passenger on the Niners' freight train, surrounded by a frighteningly good collection of talent and taking directions from one of the league's sharpest offensive minds. Both of those things can be true while also acknowledging that Purdy is more than pulling his weight during the team's 4-0 start.

While many have been waiting for Purdy's supposedly inevitable regression, he has, at least through four games, done the one thing that his detractors -- and more important, San Francisco's opponents -- didn't want him to do: get better.

That improvement was on display against the Cardinals, as Purdy went 20-of-21 for 283 yards and a touchdown, adding a rushing score for good measure. His 95.2% completion rate in that game is the best by any passer in franchise history and the fourth best by any quarterback with a minimum of 20 attempts in NFL history.

According to NFL Next Gen Stats, Purdy had a completion percentage over expectation of 28%, the highest mark by a quarterback with at least 20 attempts in a game over the past seven-plus seasons. His previous career high for a game was 5.1%.

"That's crazy," receiver Brandon Aiyuk said. "It just tells you the type of quarterback that he is and how efficient he is knowing where to go with the football."

Entering this season, it was fair to question how real Purdy's performance last season was, as the final pick of the 2002 draft completed 67.3% of his passes (114-of-170) for 1,374 yards and 13 touchdowns with a 67.5 QBR in the regular season while winning his first seven starts (including playoffs).

The Niners insisted they were true believers, but the sample was small and Purdy was coming off a torn ulnar collateral ligament in his right elbow suffered in the NFC Championship Game loss to the Philadelphia Eagles. Could he regain that form without a full offseason taking the reps in OTAs and in training camp?

The answer so far is a resounding yes. One of the biggest things that Shanahan and quarterbacks coach Brian Griese wanted to see Purdy do in 2023 was have a better understanding of when to stand in the pocket and deliver and when to take off and make something happen off schedule. The goal wasn't to take away Purdy's creativity but to deploy it better, especially since he had the league's best QBR from the pocket (74.9) in 2022.

Griese and Purdy spent time talking about what it takes to develop trust so Purdy can get through his reads and get the ball out quickly, trusting his pass catchers to be where they're supposed to be when they're supposed to be there and throwing with more anticipation.

Early returns suggest that Purdy has fully embraced that coaching point. He has improved his time before passing from 2.84 seconds (29th in the NFL in 2022) to 2.56 seconds (tied for sixth). Despite the ball coming out faster, Purdy is pushing the ball further down the field (7.2 air yards per attempt, up 0.2 from last year) and getting bigger plays (9.1 yards per attempt, up from 8.4 last year).

What's more, a whopping 48.2% of Purdy's pass attempts have gained a first down or touchdown, the highest percentage in the league. Miami Dolphins quarterback Tua Tagovailoa is second at 47.8%, but every other quarterback is at 38.5% or below.

There have even been recent signs that Purdy's deep ball accuracy is improving. Purdy was 0-of-3 on throws traveling 30-plus air yards in the first three games. Against the Cardinals, he was 2-of-2 for 76 yards.

"He's a dude who comes in and studies his film, studies his craft and makes sure he's getting better week by week," left guard Aaron Banks said. "And that's all you can ask for from a quarterback, especially a young guy who a lot of people raise him on this pedestal and he knows that he has things to get better and things to work on."

To be sure, bigger and more difficult challenges await. That starts on Sunday night (8:20 ET, Levi's Stadium, NBC) against a Dallas Cowboys defense that held Purdy to a 55.2 QBR in the playoffs last year, the second-worst output in a game Purdy has started and finished.

And the Cowboys might be even better defensively this year, ranking first in the NFL in points allowed per game (10.3), second in sacks per dropback (10.4%) and third in opponent QBR allowed (35.9).

But nobody in San Francisco's locker room seems worried that Purdy is suddenly going to regress to the mean. Quite the opposite, in fact.

"From what I see, he's doing exactly what we need him to do," left tackle Trent Williams said. "He is exactly what we need him to be. He is exactly what we thought he was and he just continues to move forward."