John Isner overpowered Bernard Tomic in four sets as the United States booked their spot in the Davis Cup World Group quarter-finals on Sunday.

Big-serving American Isner withstood a late Tomic rally to win 6-4 6-4 5-7 7-6 (7-4) and give the Americans an unassailable 3-1 lead in Melbourne, with the fifth rubber between Sam Groth and Jack Sock not played.

Isner, who saw off Groth in the opening singles match on Friday, was a class above early as top-ranked Australian Tomic looked out of touch and out of sorts at Kooyong.

Tomic had been hampered by a wrist problem heading into the first-round tie and Isner took advantage of his lethargic opponent.

Isner was eventually pegged back by Tomic, who emerged with renewed energy and focus to force a fourth set after the former saved four set points.

However, that was as good as it got for Tomic as Isner prevailed in a tie-break, closing out the match with a service winner and ace - his 49th of the clash, without double-faulting.

The USA will now meet either Croatia or Belgium in the quarters, while Australia face a World Group play-off in September.