INGLEWOOD, Calif. -- A week after Sean McVay sprinted up and down the SoFi Stadium sideline wildly celebrating highlight-reel plays, the Los Angeles Rams' coach stood still on the same sideline Sunday, appearing stunned.

"I've got to be way better for our football team," McVay said after the Rams suffered a significant letdown in a 37-20 loss to the Arizona Cardinals. "Didn't do a good enough job getting our guys ready to go."

After an emotional Week 3 win over the Tampa Bay Buccaneers, the Rams vowed that they would move on and promised -- with a Week 5 Thursday Night Football game against the division-rival Seattle Seahawks looming -- that they would not overlook the undefeated Cardinals, a team they dominated over their previous eight meetings dating to when McVay took over as coach in 2017.

They didn't back up those vows Sunday in front of a sleepy afternoon crowd.

Cardinals quarterback Kyler Murray danced in circles around the Rams' defense, utilizing an arsenal of playmakers in a lopsided victory that moved the Cardinals (4-0) into first place in the NFC West. The third-year quarterback finished 24-of-32 for 268 yards and two touchdown passes and rushed for 39 yards on six carries as Arizona gashed the Rams for 465 yards (249 passing and 216 rushing).

"The guy is a problem quarterback in this league," linebacker Kenny Young said after the game. "He's able to extend plays, make plays off of that."

But it was not solely the defense that struggled.

The offense turned the ball over twice as quarterback Matthew Stafford completed 26-of-41 passes for 280 yards and two touchdowns with an interception, and running back Sony Michel lost a fumble.

The Cardinals converted both takeaways into touchdowns.

"I just didn't make enough plays," Stafford said. "We knew it was going to have to be one of those games where kind of blow for blow, maybe at a certain point, and we put our defense in a bad spot earlier there (by) not coming away with some points."

The loss is the Rams' largest in the division under McVay since a 21-point defeat to the San Francisco 49ers in Week 17 of 2017, a game in which he elected to rest starters in preparation for the playoffs.

After Sunday's game, neither McVay, Young nor All-Pro cornerback Jalen Ramsey provided any details regarding what caused the defensive game plan to go awry in defending Murray's passing and Arizona's running game, which had Chase Edmonds run for 120 yards and James Conner rush for two touchdowns. Each reserved judgement until film review.

"We just didn't do good enough execution-wise," said Ramsey, who had two pass deflections as he split time covering receivers A.J. Green and DeAndre Hopkins with cornerbacks Darious Williams and David Long Jr.

What was clear: Murray's acute understanding of how to pick apart the defense, particularly the secondary.

In the first half, he found Hopkins for a 25-yard reception over Long, then later in the drive challenged Long again as he completed a 41-yard touchdown pass to Green to take an early 7-3 lead.

Later in the half, he found tight end Maxx Williams for a 14-yard touchdown pass in the back of the end zone, as Williams collided with safety Taylor Rapp. The score gave the Cardinals a 14-10 lead that would not be surrendered.

"There was a couple instances where we felt like we could have been better, but you got to give him credit," McVay said about Murray, who was sacked three times but was never deterred. "He's a playmaker. He's been doing this for the last couple years but it's especially been illustrated the first three weeks of this season and it was on display today."

The Rams fell to 3-1 and second in the division and now must prepare on short order for the Seahawks (2-2) and quarterback Russell Wilson, who also is known for his ability to scramble and complete downfield passes while on the move.

"I hope so," Ramsey said when asked if playing Murray could help prepare for another mobile quarterback on a short week. "We'll see, but I hope that will help. ... We didn't look great tonight, so we've got to fix that."

"We'll look at ourselves critically, we'll move forward," McVay said. "And again, part of being able to do this the right way is being able to handle the ebbs and flows."