Woodland (63) gave Koepka a run for his money, closing the gap with six birdies on the front nine, but his charge faltered with a bogey on 17 and he finished alone in second on 17-under.
A wrist injury, having partially torn a tendon in January, was expected to keep him out for 10 weeks but dragged on and Koepka conceded defeat in his race to be fit for the first major of the year after rating himself at only 80 per cent ahead of Augusta.
"To be world number one is something I dreamed of as a kid and I don't think this one's going to sink in yet", he told his post-round press conference. "I can't wait to go play again". Oddly enough, considering his status a three-time major victor and an impending No. 1, this would be Koepka's fifth Tour victory but only his second in a non-major; his only regular Tour win to date was his first, at the 2015 Waste Management Phoenix Open.
American star Justin Thomas was 16 strokes off the pace following his four-under-par 68.
However, he produced a delightful chip that disappeared straight into the cup, and when Woodland dropped a shot at the par-three 17th Koepka was virtually home and dry.
He won by four shots from compatriot Gary Woodland, who briefly shared the lead in the final round, with another American, Ryan Palmer, signing off with a ten-under-par 62 to share third position with Spaniard Rafa Cabrera Bello. "I've hit a lot of greens over the last two days, which has been nice and I just need to continue that".
"You obviously want to get off to a good start and put pressure on him as soon as you can", he said. Even for a good finish I had to go low today. Koepka has now won three of his last 11 starts on the PGA TOUR.
SHANGHAI - Danielle Kang shot a 3-under 69 on Sunday to win the LPGA Shanghai by two strokes for her second career title. "No, it would be very special, and to do it here would be nice and hopefully get to world No. 1 and cap it off with a win, I don't think there would be much better".
A final-round 66 at Bellerive Country Club lifted him to 16 under par, two ahead of Woods, to join the 14-time major victor, Gene Sarazen, Ben Hogan and Jack Nicklaus as the only players to win the US Open and US PGA in the same season.
RICHMOND, Va. - Woody Austin shot a 3-under 69 for a one-stroke victory over Bernhard Langer on Sunday in the PGA Tour Champions' playoff-opening Dominion Energy Charity Classic.