TEMPE, Ariz. — The Arizona Cardinals gave the ball to rookie Tim Hightower in two of the most critical situations in their season opener.

It was proof of how much the coaching staff believes in the youngster from Richmond, and so far he's succeeded in what's been asked of him.

"It was real nice," Hightower said. "It just showed that the coaches have some confidence in me, they believe in me a little bit, which is always good, especially for a young running back."

Hightower, who backs up Edgerrin James, gained only 13 yards in eight carries, but two of his attempts came on fourth down and were among the biggest plays in Sunday's 23-13 victory at San Francisco.

First, there was his 2-yard touchdown run on fourth-and-inches, a score that put Arizona up 20-10 with 4:03 left in the third quarter. Then when coach Ken Whisenhunt decided to go for it on fourth-and-one at the San Francisco 27, Hightower got the ball again and ran two yards for a first down.

That allowed the Cardinals to run out another 3› minutes of an 18-play drive that used up 10:08 and culminated in Neil Rackers' clinching 30-yard field goal with 1:57 to play.

Hightower, a fifth-round draft pick and the 13th running back selected, impressed the coaches in training camp, leading to the release of longtime Cardinal Marcel Shipp.

Whisenhunt said Hightower stood out in goal-line drills during camp. That led to the decision to make him the No. 1 back when the Cardinals are in critical need of a yard or two.

"When you get into that situation you go with the guy who showed you that he could do it," Whisenhunt said, "and he didn't disappoint us, obviously."

Playing behind James is an education for the 22-year-old Hightower.

"It's great," he said after Wednesday's practice. "I learn something every single day. ... I'm constantly learning. I'm constantly becoming better. I try to be quiet and just observe."

Quarterback Kurt Warner sees similarities in the two backs, neither of whom are breakaway threats.

"Tim is one of those guys that's going to go in and pound, too," Warner said. "He's not going to go backwards. He's going to put his head down and give you some tough yards in some key situations."

Hightower set Richmond career and single-season records for yardage and touchdowns in just two seasons as a starter. The Cardinals passed on more high-profile backs earlier in the draft before going with him.

He said his relatively late selection provides motivation, but he knew he could play in the NFL.

"I put the hard work in. I've been disciplined and did the workouts and applied myself," Hightower said. "I knew when I had my opportunity that I would make the most out of it. Fortunately, I was able to be here in a great situation for me, great coaching and great players."

He arrived in training camp eager to play whatever role the Cardinals had for him.

"Whether it's third down, whether it's short yardage, special teams, that's something I wanted to be good at," Hightower said.

Now that he's in the NFL, Hightower said he is taking nothing for granted.

"I'm just fortunate to be here," he said. "I'm blessed and I just want to keep taking advantage of the opportunity."