THOUSAND OAKS, Calif. -- Aaron Donald played in the season opener with peace of mind. With a six-year, $135 million extension in hand, the Los Angeles Rams star defensive tackle didn't have to worry about his future.

But even Donald's newfound security couldn't provide him with a sense of satisfaction after a victory over the Oakland Raiders.

Donald expressed disappointment in his performance after Monday night's game, and the feeling lingered on Thursday.

"I could have played better," Donald said. "I'm gonna always be my worst critique -- that's just about trying to push myself to get myself better."

Against the Raiders, Donald, the reigning NFL Defensive Player of the Year, finished with a lone tackle.

"I feel the way he did, somewhat," defensive coordinator Wade Phillips said, adding, "I want him to do better, he wants to do better, but he's still a great football player."

The NFL's reigning Defensive Player of the Year was not happy with his one-tackle performance in Week 1, which could mean bad things for the Cardinals. Ezra Shaw/Getty Images

The Rams (1-0) play the Arizona Cardinals (0-1) in an NFC West matchup on Sunday at the Coliseum. The Cardinals feature running back David Johnson, who recently signed a three-year, $39 million extension, and quarterback Sam Bradford, Donald's teammate in St. Louis in 2014.

"He's a good quarterback," Donald said. "If you don't get to him and he's back there, comfortable, it's a long day for us, so our job as a front is to get him to the ground and get some hits on him and try to make him uncomfortable back there."

In their season debut, the Rams' defensive line -- featuring Donald, Ndamukong Suh and Michael Brockers -- had a difficult time getting to Raiders quarterback Derek Carr, who often hurried to get the ball off.

"They had a good scheme against us, trying to get the ball out pretty quickly," said Suh, who finished with four tackles and a quarterback hit. "A lot of checkdowns and what not, so they didn't want to get us started."

The defense allowed 13 points in the first half, including a 10-yard run by Marshawn Lynch for a touchdown in which Lynch practically carried the Rams' defense across the goal line. The defense posted a shutout in the second half.

Scheme and game plan aside, Donald said he could have done more. He nearly recorded a sack in the first quarter, if not for a penalty. Donald made easy work of All-Pro left guard Kelechi Osemele, but he started to fall as he got to Carr. Donald hit the quarterback low and was penalized for roughing the passer.

"He made a lot of disruptions, but he is the type of guy who wants to make those sacks and tackles for losses and ultimately dominate the game," said Brockers, who had five tackles and a sack.

"It was just more, you know, I just have to rush better and do things better," Donald said. "I'm second-guessing myself on certain things."

After holding out of training camp for a second consecutive season, Donald reported 10 days before the opener. He participated in six practices, then played in 89 percent of the snaps (62) -- more than any other lineman -- against the Raiders. He also played four snaps on special teams.

Donald's physical condition was fine, he said. After all, he experienced a similar situation last season.

After holding out of training camp a year ago, Donald reported on the eve of the opener. He was activated in Week 2 and played 55 total snaps in a loss to the Washington Redskins. After that game, Donald said he was not in football shape.

This time around, he was prepared.

"I knew what to expect," Donald said. "Just trained a little different, was able to do certain things, felt a lot better last week than I did the first game when I came back -- a whole lot better. But I still feel like I could have gave more."

Donald said he was uncertain if the Cardinals would employ the same game plan as the Raiders and encourage Bradford to get the ball off as quickly as possible.

"I hope not," Donald said. "But we going to see."

Regardless, it's unlikely Donald would be content with subpar performances in consecutive weeks.

Bradford had better be on the lookout.