Jordan Spieth sees no reason why he cannot win next month’s Open Championship after emerging victorious at the US Open in stunning fashion.

The 21-year-old, who also won the Masters in April, carded a one-under 69 at Chambers Bay on Sunday to win by one stroke from Dustin Johnson, who three-putted the last hole from 12 feet.

Spieth is now on course to become the youngest golfer to win all four majors in a calendar year.

The world number two started the final round in a four-way tie for the lead with Johnson, Branden Grace and Jason Day.

He is now 7.50 to win the Open Championship at St Andrews, while world number one and defending champion Rory McIlroy can be backed at 5.25.

Spieth said: “You can’t win them all if you don’t win the first two. We’ll go to the home of golf prepared to try and win the Claret Jug.”

Spieth is only the sixth man to win the Masters and the US Open in the same year and is the youngest US Open champion since Bobby Jones in 1923.

“We really grinded this week. I didn’t have my best stuff, ball-striking, at all,” Spieth added. “We really grinded over those four to five footers and that was the difference.”

South Africa’s Louis Oosthuizen finished superbly to secure a tie for second with Johnson.

He had six birdies in his last seven holes as he carded a 67 while McIlroy posted a 66 to finish on level par.