SCOTTSDALE, Ariz. – What a week for Jon Rahm at the Waste Management Phoenix Open. The Arizona State junior carded a 3-under 68 en route to a tie for fifth place at 12-under 272, three strokes behind winner Brooks Koepka.

“Lifetime experience,” said Rahm, 20, of Barrika, Spain. “It just shows me that I’m a lot better than I thought.”

Rahm, who received a sponsor exemption into the field, made par on TPC Scottsdale's first eight holes Sunday before a bogey at No. 9 to make the turn in 36. “I was kind of mad,” he said. “On 10, I said, ‘It’s a new day, so really start over again.’ ”

He did just that, rolling in a 16-foot birdie putt there and then circling the card three more times, at Nos. 13, 15 and 17. Just as he did every day, Rahm donned a Sun Devils football jersey with his nickname – Rahmbo – on the back when he arrived at the stadium par-3 16th.

“It’s like being a gladiator,” Rahm said of playing the famed hole with its Colosseum-like setting.

Rahm battled nerves early and got off to a sluggish start in his first round. He was 3 over through his first six holes.

“I don’t think my heart has ever beaten that fast,” Rahm said. “I honestly thought I was going to pass out right on the tee.”

The whole complexion of his tournament changed at the 17th hole when he nearly aced the drivable par 4.

“If I don’t eagle that hole, I don’t know how anything would have been,” he said.

Rahm topped Phil Mickelson, who finished T-32 in 1991, for the best finish by a current member of the Sun Devils golf team in the Waste Management Phoenix Open. Rahm also is the first amateur to finish in the top 5 of a Tour event since Chris Wood placed fifth at the 2008 Open Championship.

If Rahm were a professional, he would have earned $239,400. However, amateurs can’t top-10 their way into the next Tour event, so Rahm is scheduled to catch a flight Monday to Hawaii to meet his college teammates for the Amer Ari Invitational, which begins Feb. 5. By making the cut at a Tour event, Rahm is exempt into the first stage of Web.com Tour Qualifying School in the fall. Despite proving this week that his game stacks up against the pros, Rahm hasn’t lost sight of his goal to stay in school and graduate.

“My mom and dad always preached the importance of getting an education,” Rahm said. “You have to have a career, just in case. The PGA Tour isn’t going anywhere.”