Cardinals running back Kerwynn Williams finds a crease in Sunday's loss to the Rams.

A small pad gave Kerwynn Williams' cracked ribs a measure of extra protection on Sunday, but it was a steeled resolve that proved to be the true fortification.

The Cardinals' running back refused to let the painful injury affect him, as Williams not only played but had a starring role in the 32-16 loss to the Rams. Williams carried the ball 16 times for 97 yards and was the catalyst behind a second-quarter scoring binge that helped rally the Cardinals from a 16-0 hole.

"I think you just have to go," said Williams, who was hurt last week against the Jaguars. "Honestly, if you think about it too much, it will slow you down. So you just have to stay focused on the task at hand and do what you can to get out there and play."

The Cardinals' running situation looked dicey heading into the game because Adrian Peterson was inactive due to a neck injury. While Williams had stepped up in the past, the injury complicated matters, leaving coach Bruce Arians to wonder aloud on Wednesday how his running back rotation would line up.

Williams took the majority of the carries and answered the bell, averaging 6.1 yards per rush to keep the Cardinals from getting blown out.

"Kerwynn always steps up," Arians said. "He was hurt. Every time he starts, gets 100 yards almost. He was the sparkplug to get us back in the game."

Arians was asked if he knew how much Williams would be able to give him in the game.

"Knowing Kerwynn, he was going to give us everything he had all day," Arians said.

Williams shined on a second quarter possession that got the Cardinals on the board. He broke off runs of 7, 10, 14, 19, and 7 yards to get the ball into the red zone, and Elijhaa Penny, the bigger back, finished it off with a 1-yard touchdown plunge.

The Cardinals scored again on their next possession as the run, coupled with the threat of it, kept the Rams' defense off-balance. The offensive line dominated throughout that stretch.

"They opened up a lot of big holes and made it to where I can make plays happen," Williams said. "I think that a lot of my success today is a tribute to what they did."

The Cardinals' running game wasn't as effective in the second half, and the offense eventually had to go away from it because the team fell behind. Arians said the Rams didn't do anything to limit it after intermission.

"With those plays that were eight or nine (yards), we're getting two or three," Arians said. "We didn't finish the blocks as much as we had."

While the run game tailed off, Williams' performance still helped the Cardinals outrush the Rams and average 4.9 yards per carry overall.

When the week began, Arians doubted Williams would even be available for the game, but changed his tune when the veteran showed up to practice on Wednesday. The moment of truth came Sunday -- taking live shots from defenders is drastically different than going through the motions during the week -- but Williams never blinked.

"He's pound-for-pound one of the toughest players on the team," Penny said.

It was a rare opportunity for Williams to carry the ball consistently, as he's been a reserve for the vast majority of his career. He had a fleeting chance earlier this season after David Johnson's injury, but that was extinguished when the team signed Chris Johnson and then traded for Adrian Peterson.

Williams has reverted to a backup role, seeing sporadic touches on offense and some on special teams as a return man. So when he got the call, teammate Larry Fitzgerald was not surprised to see him seize it, cracked ribs and all.

"I love Kerwynn to death," Fitzgerald said. "He's one of my favorite teammates. He's a guy who is always looked over, always trying to be replaced, always drafted over. He never allows that to affect his psyche, never allows that to affect his preparation. He's a wonderful teammate, and any time he has success, I think everybody just loves seeing him do it."