WASHINGTON (AFP) - Top-ranked Jon Rahm, the reigning US Open champion, rallied for a 5&4 victory over American Cameron Young to remain unbeaten on Thursday (March 24) at the WGC Match Play Championship.

The 27-year-old Spaniard, who fought back from two down after five holes, improved to 2-0 to lead his group entering Friday's final group-stage matches at Austin (Texas) Country Club.

"I'm confident," Rahm said. "I'm happy, feeling good. Playing good golf. It was a tricky day."

The 64-player field based upon world rankings was divided into 16 groups of four for round-robin matches. Group winners will play weekend knockout rounds.

Young birdied to win the first hole, Rahm took the second with a par, but birdies from 17 feet at the par-three fourth and seven feet at the par-four fifth put Young 2-up.

Rahm won the par-five sixth with a tap-in birdie to pull level and took the next three holes with pars to seize command.

"I just had to stay patient knowing that mine was coming," Rahm said. "That stretch, the dynamics of the match changed. From six on I played wonderful golf."

He rolled in a 17-foot birdie putt at the par-three 11th, tapped in for birdie to win the par-five 12th, took the par-four 13th on Young's bogey and halved No. 14 to close out the match.

"The wind was pumping. I kept playing solid," Rahm said. "I stayed bogey-free and he made a couple mistakes, the momentum shifted and I was able to get the win."

Rahm can advance by beating eliminated Patrick Reed in a match that will have a Ryder Cup feel.

"It's always a tough match against him," Rahm said.

World No. 2 Collin Morikawa, Norway's third-ranked Viktor Hovland and fifth seed Scottie Scheffler have a chance to topple Rahm from atop the rankings this week.

US star Morikawa tied with Sergio Garcia to share the Group 2 lead at 1-0 with a draw. Two-time Major winner Morikawa was 3-up with five to play but Garcia won the 14th on an eight-foot birdie putt, the 15th on a birdie from just inside 30 feet and the par-five 16th on a birdie putt from just inside 27 feet.

Morikawa made a nine-foot par save to tie the par-three 17th after finding a bunker and both parred No. 18.

Hovland rose to 2-0 atop Group 3 by beating American Cameron Tringale 2&1.

Ireland's Seamus Power beat winless fourth seed Cantlay 5&4, eliminating the American and reaching a group-best 2-0.

Scheffler was way left at No. 17 and made bogey to lose 2&1 to England's Tommy Fleetwood, leaving all four players in Group 5 on 1-1.

Defending champion Billy Horschel seized the Group 12 lead on 2-0 by beating US compatriot Tom Hoge 3&2.

England's 13th-seeded Tyrrell Hatton beat South Korean Kim Si-woo 1-up to seize the Group 13 lead on 2-0. Kim was way left off the last tee and lost the hole and match on a bogey.

US ninth seed Bryson DeChambeau was eliminated by a 1-up loss to England's 48-year-old Lee Westwood.

Westwood faces 49-year-old countryman Richard Bland on Friday for a chance to advance. Unbeaten Bland beat American Talor Gooch 1-up thanks to a 13-foot birdie putt at No. 17 and closing par.

"I don't need this stress at this time in my life," Bland said. "I should be taking it easy."

Canada's Corey Conners and Sweden's Alex Noren, both 2-0, play Friday for the Group 10 crown. Conners beat 10th seed Louis Oosthuizen 2&1. Noren won when England's Paul Casey was idled by a nagging back injury.

Australian Lucas Herbert sank a seven-foot birdie putt at the 18th to beat Tokyo Olympic champion and seventh seed Xander Schauffele 1-up to lead Group 7 at 2-0.

Dustin Johnson took the Group 8 lead at 2-0 by beating US compatriot Matthew Wolff 4&2.

Four-time Major winner Brooks Koepka and Ireland's Shane Lowry both won in Group 16. Koepka beat Harold Varner 2&1 to reach 2-0 while Lowry, 4-up with four to play, hung on to beat South African Erik van Rooyen 2-up to reach 1-1.

Group 11, with four Major champions, was wide open after England's Justin Rose beat American Jordan Spieth 3&2 and Australian Adam Scott drew American Keegan Bradley.

American Kevin Kisner, the 2019 winner, beat Luke List 1-up to take the Group 6 lead at 2-0.