Koepka carded a five-under round of 67, which included three consecutive birdies from the 14th hole onwards, to end four shots clear of the rest of the field.

The 27-year-old, whose previous best result at a major came when he was tied for fourth at last year's USPGA Championship, matched the score achieved by Northern Ireland's Rory McIlroy in 2011.

Japan's Hideki Matsuyama produced the lowest-scoring round on the final day as he shot a six-under-par 66 to end the tournament tied for second, along with overnight leader Brian Harman of the United States, on 12-under.

England's Tommy Fleetwood was fourth overall on 11-under-par after he hit a level-par 72 in his final round.

"We started out this year and I thought I needed to win multiple times and a major," Koepka said. 

"I'm sure someone even heard me say that. 

"I thought the way my game set up, I can win multiple times a year, I really do. 

"This is hopefully major number one and there's many more to come.

"To be in the same category as some of the guys on this trophy is unbelievable.

"This is truly special, it really is."

Koepka signalled his intention from the outset as he birdied his first two holes and the eighth, before a drop shot followed on the 10th.

The American then sunk a 10-foot putt on the 13th and then began to run away with it as his run of birdies in the late stages effectively sealed victory.

Matsuyama, the world number four, started six behind Harman but went on to post a decent clubhouse lead after a consistent round which began with three birdies in five holes.

American Rickie Fowler had also been in contention for much of the round but could only manage fifth place on 10-under-par.