Ash Barty’s path back to the World No.1 ranking was made a whole lot simpler on Saturday when Naomi Osaka was forced to retire hurt at the Cincinnati Masters.
Barty moved one win away from a return to the top WTA ranking after reaching the semi-finals, with neither Osaka nor Karolina Pliskova progressing.
Barty, the Australian top seed, engineered her second comeback in as many days, overhauling Maria Sakkari 5-7, 6-2, 6-0.
But it was a different story for current No.1 Osaka, who quit early in the third set with a left knee injury against Sofia Kenin, with the American advancing 6-4, 1-6, 2-0.
Czech third seed Karolina Pliskova, who also had a chance at the World No.1 ranking, fell to double Grand Slam champion Svetlana Kuznetsova of Russia 3-6, 7-6 (7/2), 6-3.
Osaka's injury rings alarm bells with her defense of her US Open title coming up in less than two weeks.
The Japanese star ran hot and cold in her match against 20-year-old American Kenin.
Oaska had won the second set to level the match when she first complained of apparent knee pain.
After one game of the third set, she called for the physio, who spent nearly 10 minutes in examining the problem left knee.
Osaka told reporters after the match that it was an unfamiliar pain she was experiencing.
"The thing is, my pain tolerance is really high," Osaka said.
"So that's usually why I play through things that apparently I shouldn't. So I really don't know what's going on with my leg right now.
"I was asking the physio if it was safe to play, because I really hate withdrawing. I feel like we were playing such a great match, too. It's not fair to her to just withdraw, because I feel like I'm bowing out.
"Then I was asking the physio if she thinks it's safe to play. Then I went out there. I wanted to finish the set. But I felt it wasn't safe."
With the knee heavily taped Osaka played one more game before packing it in and sending Kenin to the semis.
"This is not the way I wanted to win," the American said. "I wish Naomi a speed recovery before the Open.
"I have a lot of respect for her."
It meant Barty simply had to make the final to regain the top spot in the rankings.
No.1 not Barty's focus
Reigning French Open champion Barty said she wasn’t focusing on a possible return to the top of the rankings, but concentrating instead on playing steady tennis.
"I'm in the semis for the first time here," she said.
"I'm not thinking of the ranking at all.
"I'm playing one match at a time. If I can win matches, the ranking will take care of itself."
Greece's Sakkari came alive in the first set, battling from 5-2 down and winning 14 of the last 16 points to pocket the opener.
But Barty dug in to begin her fightback.
"I was more patient in the second and third sets. I served better, hit my spots," Barty said.
"She was playing super-aggressive in the first set.
"I made a few simple adjustments, making her play a few more balls.”