Dustin Johnson held on to beat Spain's Jon Rahm 1 up on Sunday to win the World Golf Championships Match Play crown and become the first player to win all four WGC events.
World number one Johnson was 5 up through eight holes but withstood a furious rally by the 22-year-old Spaniard, who was trying to become the youngest winner of one of the elite WGC events.
Rahm's comeback bid fell short when he was unable to birdie the 18th to extend the match. Johnson rolled in a four-footer for a par to halve the hole and seal the win.
Johnson, the reigning US Open champion, won the WGC HSBC Champions in 2013, the WGC Cadillac Championship in 2015, the WGC Bridgestone Invitational in 2016 and the WGC Mexico Championship earlier this month.
His wins in Mexico and on Sunday in Austin, Texas, saw him join Tiger Woods as the only players to win back-to-back WGC titles.
The victory capped a dominant week for Johnson, who never trailed in any of his seven matches.
Johnson took the final by the throat when he won four straight holes from the third through the six as the ever-more frustrated Rahm struggled with the putter.
But Rahm kept his nerve after falling 5 down when Johnson won the eighth with a par.
And the young Spaniard, who won his first US PGA Tour title at Torrey Pines this year, won the 13th, 15th and 16th with birdies -- rolling in a clutch 32-footer at the 16th.
After both parred the par-three 17th, they went to 18 with Johnson 1 up.
Johnson hadn't been beyond the 16th hole until Sunday. He also had to hang on for a 1 up win over Japan's Hideto Tanihara in the semi-finals on Sunday morning.
"I definitely didn't play my best today in the first match or the second," Johnson said. "So, to win both those matches not having my best stuff is definitely a positive.
"And I'm definitely proud of the way I hung in there and played tough and just tried to never give away holes, which I felt like I did a pretty good job of."
Johnson's two latest WGC triumphs follow a victory in the Genesis Open at Riviera in February that propelled the American to number one in the world. He's the first player since Rory McIlroy in 2014 to win three consecutive US PGA Tour starts.
"I've got a lot of confidence now -- confidence in my game and confidence in myself," Johnson said.
Rahm's bogeys at the third and fourth saw Johnson take a quick lead, which the American built on with birdies to win the fifth and sixth holes before another bogey from a clearly frustrated Rahm at the eighth saw Johnson go 5 up.
"I was trying to do the best I could, but just things weren't happening, unfortunately for me," Rahm said of the front nine.
Rahm narrowed the deficit when he won the ninth with a par, and won the 10th when Johnson three-putted for bogey.
After both bombed their drives more than 400 yards down the fairway at the 12th, Johnson ended up with a two-putt birdie while Rahm's second shot landed in a bunker and he ended up with a par.
- Proud Rahm -
At 13, Rahm drove the green an two-putted for a birdie that left him just 3 down again. He cut the deficit with another birdie at 15, then rolled in his birdie bomb at 16 after recovering from a tee shot into the trees.
"I'm very proud of what I did, very proud for what I stood for on the course," Rahm said. "So honestly, as sad as I might emotionally feel, I'm extremely happy with what I did."
Rahm had beaten Bill Haas 3 and 2 in the semi-finals, and Haas went on to beat Tanihara 2 and 1 in the consolation final.
Tanihara joined Toru Taniguchi as the lone players from Asia to reach the semi-finals of the event, and he came away from an outstanding week with a Masters berth.