Australia ended their Hopman Cup title defence without a single tie win to their name after losing 2-1 to the US on Thursday night.

Australian firebrand Nick Kyrgios has revealed he has a bone issue in his left knee, but insists it won’t stop him from causing some damage at this month’s Australian Open.

The worst of Kyrgios was on display on Thursday night when he put in an insipid display during a 6-2 6-2 Hopman Cup loss to American Jack Sock.

Shot of the year, @JackSock! Oh wow 👏🔥 #HopmanCup pic.twitter.com/OVWMRsCEIm

— Gaspar Ribeiro Lança (@gasparlanca) January 5, 2017

Australian Daria Gavrilova levelled the tie at 1-1 with a fighting 6-3 4-6 7-5 win over world No.36 Coco Vandeweghe.

But the US prevailed 4-1 4-1 in the Fast4 mixed doubles, with WA’s Matt Ebden replacing Nick Kyrgios in the match.

The US will take on either Switzerland or France in Saturday’s final.

 – Justin Chadwick

Kerber upset in Brisbane

Meanwhile a rusty Angelique Kerber has suffered a worrying stumble ahead of her Australian Open defence with a quarter-final loss to Elina Svitolina at the Brisbane International.

The German world No.1 only showed glimpses of her best, often when under pressure, as she succumbed to Svitolina 6-4 3-6 6-3 at Pat Rafter Arena on Thursday night.

Angelique Kerber in action at the Brisbane International. Photo: AP/Tertius Pickard

Kerber was expected to roll on and set up a US Open final rematch with Karolina Pliskova when she dominated the second set but the Ukrainian sixth seed lifted her game superbly in the clutch moments.

In a thrilling final set, world No.14 Svitolina came from a break down to win five of the last six games to progress through to the semi-final against Pliskova on Friday night.

Elina Svitolina of Ukraine returns during her quarter-final win against Angelique Kerber. Photo: AAP/Dave Hunt

Kerber had hoped to go one better than last year in Brisbane where she lost to Victoria Azarenka in the final.

But Svitolina, who beat Serena Williams at the Rio Olympics as well as Kerber in their last encounter in Beijing, showed from the outset the dual grand slam winner would not have an easy night.

Kerber struggled on serve 24 hours earlier against local wildcard Ash Barty and again battled with her accuracy but stepped up after losing the first set.

She had the momentum going into the final set and it would be a concern ahead of the Australian Open that she couldn’t contain the Ukrainian who lifted brilliantly in an imperious finish.

Kerber is entered to play in Sydney next week where she will again be the top seed.

World No.1 #Kerber was shocked on Thursday night at #BrisbaneTennis.

Here's how #Svitolina did it: https://t.co/FwpvEVTlNb

— Brisbane International (@BrisbaneTennis) January 5, 2017

Kerber denied the loss would affect her preparations or confidence for Melbourne Park as grand slams were “completely different”.

“It was still a good match for both of us,” she said.

“We really played at a high level tonight.

“I’m happy with my start (to the year). Of course I’m obviously disappointed with how I lost in the quarters.

“(But) I can take the positives out of the tournament.”

– Jim Morton