MEMPHIS, July 29 — A potential blockbuster bout between Brooks Koepka and Rory McIlroy turned instead into a technical knockout as the American clinched an emphatic three-stroke victory at the WGC-St. Jude Invitational in Memphis yesterday.

Koepka proverbially stomped on McIlroy's throat early in the final round and never eased up on his out-of-sorts rival at TPC Southwind in an emphatic demonstration of why he is world number one.

He sank a series of clutch putts and carded a five-under-par 65 for his first victory in any of the four annual events that comprise the World Golf Championships series.

Koepka, who started the final round one stroke behind McIlroy, finished at 16-under 264.

It was the first time that Koepka and McIlroy, both four-times major winners, had been paired in a final round.

Yet McIlroy missed a short birdie putt at the third hole from inside four feet and never recovered, his body language the only evidence needed that he was not quite on-song.

The Northern Irishman did not make a birdie until the 14th hole and ended up shooting 71 and finishing equal fourth, a distant five shots adrift of Koepka.

American Webb Simpson (64) claimed second place on 13-under, a stroke ahead of Australian Marc Leishman (67). — Reuters