190 King Arthur Terrace, Tennyson QLD 4105, Australia, 5 April 2017 | AAP

Jack Sock has seen the best and worst of Nick Kyrgios and is bracing for more of the former in Australia’s Davis Cup quarterfinal tie against the United States.

World No.15 Sock last faced good friend Kyrgios – who is one spot lower in the rankings – in January’s Mastercard Hopman Cup, winning 6-2 6-2 in just 49 minutes.

Kyrgios was slammed for a perceived lack of effort and energy in that match but revealed afterwards he had been battling a bone issue in his left knee.

The 21-year-old Aussie then had a meltdown at the Australian Open a couple of weeks later but has barely put a foot wrong since, and goes into the Davis Cup match-up in Brisbane in career-best form.

Sock suspects it is because Kyrgios might have finally come to grips with his mental demons – a scary prospect for world tennis.

“He wasn’t 100 per cent healthy in that match in Perth, so we can’t really go off that,” Sock said. “The skill and talent has always been there, everyone knows that.

“Mentally he’s doing a lot better job on court, it seems like he’s letting things go a little better. If he’s on that day and into it, he’s tough.”

If Kyrgios is in career-best form, than so too it seems is Sock. The talented American has taken out titles in Auckland and Delray Beach to start the year but if the Americans are confident they’re not showing it.

In fact they were so keen not to create any unnecessary headlines at yesterday’s press conference that they were caught whispering “generic answer, generic answer” to each other while reporters posed questions.

US captain Jim Courier did not reveal who he would select for singles play and neither did Australia’s captain Lleyton Hewitt, both preferring to keep their cards close to their chest ahead of tomorrow’s draw.

“I feel really good about any combination with these guys. I think we can put a good team forth. There’s all kinds of factors – form, health, momentum, all those things matter,” Courier said.

If both teams stick with their incumbent players, Friday would see Kyrgios face John Isner and top-ranked American Sock against Jordan Thompson.

That would leave Sam Groth and John Peers to battle Sam Querrey and Steve Johnson in the doubles.

Kyrgios has not played in Brisbane since he was beaten in qualifying as a 17-year-old at the 2013 Brisbane International.

“I love Brisbane. Sam has had some great results here, Thommo has played well here, Peersy has played some unbelievable doubles,” Kyrgios said. “I’ve practiced here a lot. My girlfriend (Ajla Tomljanovic) was based here, I’m used to it. I’m really looking forward to getting out here.”