Youngster Naomi Osaka showed why she is regarded as a star of the future with a brave victory over Anastasia Pavlyuchenkova as Russia beat Japan 2-1 at the mixed teams Hopman Cup in Perth on Thursday.

Osaka, ranked 68th in the world, withdrew from her previous match due to illness and appeared to be struggling physically at various times during the match, but still managed to edge past the world number 15.

Both sides were already out of finals contention and Russian Karen Khachanov then squared the Group B tie with a comfortable win over Yuichi Sugita in the men's singles.

The Russians then secured their first win of the tournament with a decisive victory in the mixed doubles.

The match between Osaka and Pavlyuchenkova featured a host of momentum changes as the form of both players ebbed and flowed, and the Japanese woman struggled with her health.

Osaka started confidently and took the first set, but she required medical attention while leading 3-2 early in the second set.

The 20-year-old, who was named the WTA Newcomer of the Year in 2016 and has been ranked as high as 40th, appeared distressed and dropped the next four games as the Russian levelled the match.

Osaka seemed to be fading, but then came out and broke Pavlyuchenkova's serve early in the third, only for the Russian to break back in the fourth game.

The set went to a tie-breaker and Osaka surged to a 4-0 lead, but then dropped the next five points in succession.

However, she again dug deep and earned her first match point, crunching a forehand winner down the line to secure a hard-earned 6-4, 3-6, 7-6 (7/5) win.

She was pleased to be able to eke out the victory given the circumstances.

"Not so well, to be honest," Osaka said when asked how she was feeling after the match.

"But I am really happy I was able to play somewhat well in my last match.

"To play against someone so good and not be 100 percent and still win, I am proud of myself."

It capped a tough week for her opponent though, with Pavlyuchenkova unable to win a singles match in her three outings.

Ranked 45th in the world, Khachanov finally notched his first singles win of the week.

After losses to top 10 duo Roger Federer and Jack Sock in his previous singles outings, the towering Khachanov was dominant against Sugita, breaking the Japanese player's serve five times.

"We had a tough group and I had a tough two (singles) matches, but I think I played well," he said.

"Tactically I played a little bit different and I am happy to get the win today."

The Russian were far too good in the Fast4 mixed doubles, winning 4-1, 4-0.