The 49ers' defense will be in for a tougher test against Kyler Murray and the Cardinals

SANTA CLARA, Calif. — A matchup with the offensively challenged New England Patriots was just what the San Francisco 49ers' defense needed to get back on track.

A better test of whether those early season struggles were a temporary blip or a more concerning problem will come Sunday when the Niners (2-2) host Kyler Murray and the Arizona Cardinals (1-3).

“He's hard,” San Francisco defensive coordinator Nick Sorensen said about dealing with the dual threat from Murray. “Those guys are hard to deal with, because he does have the arm strength and he can escape like a freaking punt returner. He’s got elite quickness and doesn’t have to have his feet set to throw the ball. So you have to be disciplined. ... It's one of those track shoe-type days.”

San Francisco had six sacks and two takeaways last week when the Niners shut down the Patriots after allowing 6.1 yards per play the first three games.

Now they have to deal with Murray.

Murray looks far more comfortable running Arizona's offense this year than he did a year ago, when he came back late in the season from a knee injury. But the performance still has been a bit up and down.

He showed flashes in the opener against Buffalo and then was at his best the following week in a victory over the Rams, in which he threw for three TDs and made big plays with his feet.

Murray has been less productive the last two weeks with the Cardinals held to 27 points in losses to Detroit and Washington, adding urgency to this week's game for Arizona.

“I have to be better,” Murray said. "To go out there and put 14 points up, that’s not the standard that we hold ourselves to. I feel like I’m surrounded by a lot of great players, so I would never expect us to go out there and put up 14 points. We don’t practice for 14 points, but this is the NFL. It is not easy, and I definitely expect to have a better week this week.”

Scrambling Purdy

San Francisco quarterback Brock Purdy will never be compared to Murray as an athlete, but he has shown an ability to make plays with his feet this year. Purdy has done a good job extending plays by scrambling and turning them into big passes down the field. He also has run more than he did last year, with eight first downs on scrambles and keepers.

“I think that’s an overlooked part of his game,” Cardinals coach Jonathan Gannon said. “Sometimes he looks like Houdini back there. It’s hard to get him on the ground, too. Not being a quote unquote, one of those guys that you talk about as a mobile quarterback, he’s very mobile.”

Murray-Harrison connection

The Kyler Murray-Marvin Harrison Jr. connection has been pretty much everything the Cardinals could hope for through four games. Harrison — the No. 4 overall draft pick out of Ohio State — has caught 15 passes for 243 yards and four TDs, showing a knack for making tough catches in the end zone.

The four TDs lead all rookies and is tied for the overall NFL lead with Minnesota’s Justin Jefferson. Gannon said Harrison’s best game was last week against the Commanders.

“I thought he launched really well off the line of scrimmage,” Gannon said. “I thought his route depth and his execution to detail, his routes were really good. I thought he won a bunch of one-on-ones. He was open a couple times, and the ball didn’t find him, but I thought he was winning at a high level.”

Big-play Fred

Niners linebacker Fred Warner has been delivering game-changing plays all season, with his 45-yard interception return for a TD last week against the Patriots just the latest. Warner has two interceptions, three forced fumbles and a sack through four games as he has elevated the play that made him an All-Pro the past two seasons to an even higher level.

“I feel like he’s been playing like the MVP of the whole league, definitely Defensive Player of the Year so far,” cornerback Charvarius Ward said. “If he keeps it up, it will be a legendary season for him.”

Warner sat out the second half last week with an ankle injury but hopes to be able to play on Sunday.

Run over

One big reason the Cardinals have lost their past two games is a porous run defense that allowed 187 yards to the Lions and a season-high 216 to the Commanders. It’s unclear if Arizona has the personnel to reverse the troubling trend. DL Justin Jones was one of the team’s most important free agent signings, but he’s out for the year with a triceps injury. Rookie first-rounder Darius Robinson was also supposed to beef up the defensive line, but he hasn’t played yet this season because of a calf injury.

“We haven’t done a good enough job stopping the run, so we’re playing behind the eight ball on defense all day and it’s a hard way to go,” Gannon said. “... We do have to do the little easy things better. Set edges, tackle, get off blocks and be in the right spot.”

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AP Sports Writer David Brandt in Glendale, Arizona, contributed to this report.