Federer's hilarious mid-match compliment from Aussie fan

Roger Federer appeared rather chuffed after receiving a hilarious compliment from the crowd during his Hopman Cup clash.

Federer linked with Swiss teammate Belinda Bencic to beat Russia 3-0 on Tuesday night, with Federer downing Karen Khachanov 6-3 7-6 (10-8) in front of 13,943 fans - a record crowd for the mixed-teams event.

And one member of the crowd made her feelings known throughout Perth Arena when she shouted out a huge compliment during the second set.

"You're beautiful Roger!" she bellowed, just as Federer was preparing to serve.

Federer reacted brilliantly. Image: Channel 7

The Swiss legend heard the compliment and turned his head as if to say "well yes I am", before waving a polite thank you.

The rest of the packed crowd loved the off-beat moment, laughing along with Federer.

Bencic secured the tie with a 6-1 3-6 6-3 win over Anastasia Pavlyuchenkova in a match that almost lasted two hours.

The result means Switzerland and the US will battle it out for a spot in the final when they meet on Thursday night.

Federer is due to meet Jack Sock on Thursday night in the men's singles rubber.

But the American is under an injury cloud after retiring from his match against Japan's Yuichi Sugita on Tuesday with a hip problem.

"I think he'll be fine," Federer said of Sock.

"There was no reason for him to take a major chance on his health so short before the Australian Open (in his match on Tuesday).

"We'll see all the players having this kind of a thought moving forward in the next 10 or 12 days, because you don't want to get hurt now.

"I think he should be OK with a day's rest. At least I hope so."

Sock is ranked eighth in the world and will give Federer his biggest test of the summer so far.

with AAP