The American joined Tiger Woods, Jack Nicklaus, Jordan Spieth and Rory McIlroy in the select group of players who won two majors before turning 25.
Louis Oosthuizen leads the way at Royal St. George, with Jordan Spieth and Brian Harman a shot further back.
World No. 1 Jon Rahm is the bookmakers' favorite as he looks to win a second consecutive major.
The reigning PGA Championship winner shot 4-over par in the opening round, while three-time major winner Jordan Spieth finished at 6-over par.
The third major of the season gets underway at Torrey Pines on Thursday with Jon Rahm as the bookmakers' favorite.
Canada's Corey Conners leads by two strokes after shooting a 5-under par 67 in the first round, with Brooks Koepka and Phil Mickelson two and three shots behind.
Rory McIlroy is the bookmakers' favorite to win the second major of the season, followed by Jordan Spieth and Jon Rahm.
The second major of the season gets underway on Thursday at Kiawah Island Golf Resort in South Carolina.
American Xander Schauffle made a dramatic comeback on the back nine, but triple bogeyed the 16th hole. American Will Zalatoris finished second by one stroke.
The pairings and tee times are set for the final round at The Masters on Sunday.
Four players are tied at second, four strokes behind Hideki Matsuyama. Jordan Spieth is six strokes back.
Dustin Johnson missed the weekend cut, but he'll be there Sunday to don the green jacket on this year's champion. Justin Rose leads after two days and Jordan Spieth is charging.
England's Justin Rose leads the field by four shots after carding a 7-under-par 65 on Thursday, while defending champion Dustin Johnson finished a 1-over-par.
The field at Harbour Town, South Carolina, features eight of the current top 10 players in the world.
Rory McIlroy is the bookmakers' favorite, followed by Bryson DeChambeau, Justin Thomas and Jon Rahm.
Harold Varner III leads the field at 11-under, one shot ahead of Jordan Spieth and Bryson DeChambeau.
Tiger Woods makes his first PGA Tour start of the season at Torrey Pines, playing the first two rounds alongside world No. 3 Jon Rahm and Collin Morikawa.
Justin Thomas and Jason Kokrak lead the BMW Championship by one shot after the first round at Medinah, Illinois.
Rory McIlroy, Brooks Koepka and Patrick Reed will play alongside each other for the first two rounds in Medinah, Illinois.
World number one Brooks Koepka and Rory McIlroy are the joint-favorites ahead of the second event of the FedEx Cup playoffs.
World number one Brooks Koepka is the bookmakers' favorite to win at Liberty National Golf Course, followed by Rory McIlroy and Jon Rahm.
Rory McIlroy and Brooks Koepka are again paired alongside each other, while Tiger Woods tees off alongside Scott Piercy and J.T. Poston .
Brooks Koepka and Rory McIlroy will play alongside each other in the first two rounds at TPC Southwind in Memphis.
The 148th edition of the oldest golf major in the world gets underway on Thursday at Royal Portrush Golf Club in Northern Ireland.
The final major of the season gets underway on Thursday at Royal Portrush Golf Club in Northern Ireland.
The 148th edition of golf's oldest major takes place in Northern Ireland this weekend for only the second time since 1951.