ST. LOUIS - There were plenty of rooting interests on Sunday during the final round of the 100th PGA Championship. Most observers weren't backing Brooks Koepka, the two-time defending U.S. Open champion who started the day at Bellerive Country Club in St. Louis with a two-shot lead.

Plenty of fans were behind Adam Scott, the 2013 Masters Tournament winner, as he battled Koepka through the final holes while carrying the mantle of fallen Aussie comrade Jarrod Lyle, who died this week after a lengthy battle with cancer.

Even more were rooting for plucky defending PGA Championship winner and world No. 2 Justin Thomas, who was in the hunt until he lost his focus over the final five holes.

And then there was the multitude that roared in utter delight when Tiger Woods made a run up the leaderboard, all but urging the 14-time major champion into contention as he battled his swing through the front nine and his stamina down the stretch.

Through it all, Koepka was calm, making shot after shot when it was needed the most.

Koepka shrugged off challenges from Woods, in a turn-back-the-clock performance, and a resurgent Scott to capture the Wanamaker Trophy.

Koepka signed for a 4-under-par 66 on Sunday and finished at 16-under 264, two strokes clear Woods, who has won this event four times, and another shot ahead of Scott. Woods fashioned a round-low-tying 64 on Sunday to finish at 14 under while Scott shot a 3-under 67 with a bogey on the closing hole.

A 28-year-old Florida native, Koepka joined Gene Sarazen, Ben Hogan, Jack Nicklaus and Woods as only players to win the U.S. Open and the PGA in the same season.

Koepka set the PGA Championship's 72-hole scoring record at 264. The old mark of 265 (15 under par) was established by David Toms in 2001 at Atlanta Athletic Club's Highlands Course.

Koepka now has three wins in the past seven major championships - and he didn't play in this year's Masters because of a wrist injury.

The victory Sunday was just the fourth of Koepka's career, with the only non-major title coming at the 2015 Waste Management Phoenix Open. He captured the 100th PGA Championship in his 100th career start.

On his ability to come through on the big stage, Koepka told CBS Sports after accepting the trophy, "I think it's my focus. I don't know what it is, but I need to take it over into regular Tour events as well.

"For some reason, the majors just get my attention. Every shot is so important, and when you're out here grinding away, firing at the flags, firing at the middle of the greens, you just have to be very patient. And I seem to do a good job of that in the majors."

Stewart Cink, the 2009 Open Championship winner, shot a 67 on Sunday and finished in a tie for fourth with Spain's Jon Rahm (68) at 11 under.

Thomas Pieters of Belgium (66), reigning Open champion Francesco Molinari of Italy (67), Thomas (68) and first- and second-round leader Gary Woodland (69) ended up tied for sixth another stroke in arrears.

While everyone was focused on Woods and Koepka, Scott stayed in contention, canning midlength putts on the 12th and 13th holes to climb into a tie for the lead at 14 under.

Koepka broke the deadlock when he rolled in an 8-foot birdie putt on the 15th to move to 15 under. He then ripped a 4-iron to within 7 feet on the monster, 237-yard par-3 16th and calmly rolled in the putt to build his lead to two strokes with two holes to play.

Scott missed a 7-foot birdie putt on the par-5 17th that would have created plenty of drama on the closing hole. Instead Koepka went to the 18th with his two-shot lead intact. He finished with six birdies and two bogeys in the final round.

"I was feeling really good out there, but I just missed putts on 14 and 15 and Brooks made them, and my momentum was gone," said Scott, who produced his first top-10 finish of the season. "I didn't play the last two holes very well. I had high hopes for today-I'm definitely playing a lot better, and that will be important with the playoffs coming up."

Woods had four birdies and a bogey on the front nine, making the turn at 32, and was within one shot of Koepka's lead when he began the back nine. He left a 28-foot putt for birdie on the 11th short on the lip of the hole before jumping into a tie for second at 12 under with a 5-foot birdie putt on the 12th.

Woods then put a charge into the grounds with a walk-it-in birdie from 9 feet on the par-3 13th that moved him to within one of the lead. Woods lipped out a par putt on the 14th after his tee shot found the deep rough to the right of the fairway, dropping him two shots off the pace set by Koepka and Scott.

Then Woods responded in vintage style, stiffing a 9-iron from 164 yards to 2 feet on the 15th and birdieing the hole to pull back to within one. His birdie on the closing hole brought him up to second, serving notice that he can continue to be a force in major championships.

"I played hard," Woods told CBS Sports. "Bit of a struggle with my game today. I was hanging in there, just grinding it out and trying to make as many birdies as possible. This golf course was giving it up, and I made a little bit of a run. ...

"I never quite got to the lead. I was always trailing. It was a golf course in which I couldn't sit still and make pars and be OK with it. I had to keep making birdies."

Koepka was well aware of Woods' charge.

"The crowds here, they definitely let you know what's going on," Koepka told CBS Sports after accepting the trophy. "You (fans) are awesome, first off. The beginning of the back nine, I could hear all of the roars. When Tiger started making his little run, and then Scotty (Adam Scott) made his run, it got quite loud. It was quite fun, it was enjoyable. It was enjoyable to play in front of fans who love golf and who are cheering for us."

Thomas, playing three groups ahead of Koepka, pulled into a tie with for the lead at 12 under with back-to-back birdies on the 10th and 11th holes. However, Koepka reassumed the top spot with a birdie on the eighth and another on the ninth and turned for home at 14 under and two up on the field.

"I felt like I had a lot of positives from today," Thomas said. "I feel like I had a great chance to win this tournament. I love being in that position, I felt very comfortable, I just flat out didn't execute the shots. So that's a bummer."

Rafa Cabrera Bello of Spain and Tyrrell Hatton of England tied for 10th place at 9 under as they joined Woods in shooting 64s on Sunday.

Three-time major winner Jordan Spieth finished in a tie for 12th at 8 under after a 66 on Sunday. World No. 1 Dustin Johnson carded a 69 in the final round, leaving him in a tie for 27th.

The PGA Tour heads to Greensboro, N.C., next week for the Wyndham Championship at Sedgefield Country Club.