BRISBANE (AFP) - A much happier Nick Kyrgios sent Australia into the Davis Cup semi-finals when he beat American Sam Querrey in the first of the reverse singles in Brisbane on Sunday (April 9).

Kyrgios' 7-6 (7-4), 6-3, 6-4 win gave the Australians an unassailable 3-1 lead over the US before John Isner won the dead rubber 7-6 (7-5), 6-3 over Sam Groth.

The controversial Kyrgios, whose on-court behaviour has led to a host of criticism from fellow players, commentators and fans, was the model of decorum and dedication in his two matches.

The 21-year-old revealed later that Australian captain Lleyton Hewitt had asked him to be the team's leader, and he had been happy to accept the challenge.

Kyrgios, who once confessed to not enjoying the game, said he was in a much better place now and his recent results reflected his mindset.

"I'm playing better, but I'm just in a happier place," he said. "I'm going out and playing the game how it's meant to be played.

"I haven't been going back to the hotel hating the game or just trying to get through every day.

"I'm trying to get better every day, and that's a massive difference."

Kyrgios pushed eventual champion Roger Federer to the brink in the Miami Open semi-finals last week and has made the final four in three of his last four tournaments.

He said that during this run of good form, he always had one eye on the Davis Cup.

"I've been looking forward to this tie for a long time now," he said. "I always had one eye on it. When I was in the States I always knew I had to come here and play two big matches.

"It's a bit (of) a relief. It's one thing to say I've been preparing for it, but to actually deliver, it feels pretty good.

"Obviously the way I've been playing for the past two months has created an expectation these couple of days," he added. "It was a lot of relief to get through."

Kyrgios and Jordan Thompson put Australia in the driving seat when they won the opening singles on Friday, with Thompson scoring an upset win over American No. 1 Jack Sock before Kyrgios downed Isner.

The Americans hit back in the doubles on Saturday, with Sock and Steve Johnson beating Groth and John Peers in five sets.

But Kyrgios, who has been in superb form this week, was too good for Querrey, and wrapped up the match in two hours and five minutes.

The victory will go a long way to winning over an Australian sporting public who have grown tired of the world No. 16's behaviour.

His past was all but forgotten by the packed crowd at the Pat Rafter Arena, who chanted his name as he ran to Hewitt and carried him around the court in delight.

Australia will now play either Belgium away or Italy at home in September's semi-finals. Belgium lead Italy 2-1 in their quarter-final tie in Charleroi.