190 King Arthur Terrace, Tennyson QLD 4105, Australia, 8 April 2017 | AAP

Nick Kyrgios has continued his stellar form to defeat big-serving American John Isner in straight sets and put Australia on the brink of the Davis Cup’s final four.

Kyrgios won 7-5 7-6 (7-5) 7-6 (7-5) against Isner at Brisbane’s Pat Rafter Arena to give Australia a commanding – and unexpected – 2-0 lead in the World Group quarter-final tie.

After Jordan Thompson’s shock victory over Jack Sock in the opening rubber, it leaves them just one win away from a semi-final date against Italy or Belgium in September.

Kyrgios – coming off arguably the best stretch of his career to date – looked confident and untroubled throughout.

He clawed back from 5-2 down in the deciding tiebreaker to finally end Isner’s resistance after nearly two-and-a-half hours.

“The crowd was unbelievable. Let’s hopefully close it out tomorrow,” world No.16 Kyrgios said on court after the win. “He’s one of the best servers in the world, a proven player.

“I’ve been putting my head down and I returned really well. I’m really happy to get the win.”

It was a mature display from Kyrgios, who won through superior court coverage and generally stronger shots.

He gave away a whopping 15cm in height but still managed to outserve Isner, slamming 20 aces to 15, many of them coming at key moments.

World no.23 Isner made a sizzling start and raced to a 3-0 lead in the first set.

But Kyrgios, 21, recovered to win it 7-5 and then held his nerve in the second-set tiebreaker.

Earlier, Thompson scored the biggest win of his career to date over top-ranked American Sock, claiming a tense 6-3 3-6 7-6 (7-4) 6-4 victory.