Killing time during a three-hour rain delay Sunday, Phil Mickelson ribbed Daniel Berger about having won the PGA Tour rookie of the year award without a victory.

That was a bit of a sore spot for the ultra-competitive 23-year-old Floridian.

Berger answered once the thunderstorms ended by winning the FedEx St. Jude Classic for his first title. He shot a 3-under 67 to hold off Mickelson, Steve Stricker and Brooks Koepka by three strokes.

"To kind of get it done today means a lot," Berger said.

Berger had never been in a final pairing until Sunday. First Mickelson needled him in the players' dining area while everyone waited out the lightning. Then, Mickelson, with his 42 career PGA Tour titles, closed within a stroke on the back nine. Berger responded with birdies on three of his next four holes, highlighted by a 32-foot putt on the par-3 14th that pushed his lead to 13 under.

He finished at 13-under 267. He became the 13th first-time winner on tour this season and took home the winner's check of $1.1 million in the 50th start of his career.

"To do that with so many great players, Hall of Famers behind me, it's something that I'll never forget and I just love the way I hung in there and was able to get it done," Berger said.

Mickelson and Stricker shot 67, and Koepka had a 66. Dustin Johnson had a 63, setting the back-nine record with a 29, to finish fifth at 9 under.

Mickelson complimented Berger for playing the back nine really well and said he enjoyed being in contention even though the veteran couldn't quite catch the youngster.

"For the most part I hit a lot of good shots, played pretty well and seems, it almost feels like U.S. Open came a week early to finish another second place," Mickelson said.

Berger also became the fourth first-time winner at this event in the past six years and 10th overall in Memphis.

Now he will head to Oakmont trying to do something no one has ever done before by following up a tour title by winning the U.S. Open. Only 11 have ever won a major after winning on tour, and Rory McIlroy was the last when he won the PGA Championship the week after taking the WGC-Bridgestone Invitational in 2014.

He'll be arriving pretty confident too.

"When I played in the Masters for the first time I think I finished 10th, five shots behind and didn't really play that great," Berger said. "So, you know if I can go in there next week and play good, then obviously I have what it takes to get the W."

The thunderstorms slowed down the confident Berger, and only for a hole. He had hit only hit three shots when the horn sounded. Play finally resumed at 4 p.m., and Berger resumed by two-putting from 10 feet on No. 1 for bogey.

Berger already had finished second twice with a total of nine top 10s in his young career. He shook off the bogey by stringing together four straight pars with Koepka catching him atop the leaderboard at 9 under before bogeying No. 8.

He birdied Nos. 6 and 11 to make the turn at 11 under.

He stumbled on No. 10, two-putting from 10 feet again for bogey. Mickelson went to 9 under with two birdies on his first three holes on the back nine, which included a 44-footer on the par-4 12th. Then Mickelson's putter failed him as he just missed from 11 feet on No. 13 and 17 feet on No. 14 chasing his first win since the 2013 British Open.

Berger had no such issues as he rolled in putts of 8 feet on No. 12, the 32-footer on No. 14 — the same hole he put his tee shot into the water Saturday and double bogeyed — and a 22-footer on No. 15. That proved more than enough margin as Mickelson birdied the par-5 16th.

Johnson rebounded from a 73 by shooting the best round this week before heading to Oakmont. He chipped in for eagle on No. 16 from 16 feet and holed out from 22 feet on No. 18 to set the back-nine record. That put him a stroke back of Berger who had 11 holes to play, but Johnson felt good about his game with the U.S. Open next.

"On the back nine, I had great looks on every hole," Johnson said. "Struck it a little better. I got a little sloppy with my setup the first couple days. Caused me to mishit some shots. I'm real comfortable, real confident going into next week."