Perth Arena, 4 January 2017 | AAP

Australian No.1 Nick Kyrgios has told everyone to “relax” about his niggling knee injury, saying it’s nothing serious and won’t hinder his Australian Open campaign.

But Australia’s Hopman Cup title defence is over after they suffered a surprise 2-1 loss to the Czech Republic on Tuesday night.

Despite appearing to hobble from time to time in the first set, Kyrgios was able to seal a relatively straightforward 7-5 6-4 win over Adam Pavlasek on Tuesday night.

“I was feeling it a little bit. But as the match went on and I got warmer (it was ok),” Kyrgios said.

“That’s the key to the knee – I’ve just got to get warm before I run out.

“I didn’t really have too much time to warm up before this match. I was in the physio getting it taped, and I ran out of time.

“So next match I’m going to do a better warm up and go out there with a bit of sweat and warm it up a little it.”

Daria Gavrilova then had the chance to give Australia an unassailable 2-0 lead in the tie against the Czech Republic. But the world No.25 succumbed to Lucie Hradecka in an epic three-setter, going down 4-6 6-4 6-4 in a match that lasted over two hours.

It meant Australia, who lost their opening tie 2-1 to Spain, needed to win the Fast4 mixed doubles in order to stay in the hunt for a berth in Saturday’s final.

But Kyrgios and Gavrilova succumbed 3-4 4-3 4-2.

The result means that the US, who posted 3-0 wins over the Czech Republic and Spain, are guaranteed a spot in the final from group B.