The women’s world No 1 ranking could soon change hands for the first time in 18 months.
Ashleigh Barty has been top of the rankings since September 2019, a run of 62 consecutive weeks. However, the Australian could lose her position at the top after the conclusion to the Miami Open this week.
World No 2 Naomi Osaka is bidding to dislodge Barty, and moved into the fourth round of the tournament for the first time after a walkover win over qualifier Nina Stojanovic.
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Osaka, who is on a 23-match winning run, is 1,351 points behind Barty in the rankings, but there are adjustments to the WTA ranking system after Miami that could see the Australian lose points.
The new rules, which are to account for the impact of the Covid-19 pandemic last year, will see ranking points from tournaments in 2019 begin to drop off, either 104 weeks after the tournament was played in 2019 for those tournaments being played in 2021, or, for those events not scheduled in 2021, when the tournament is next played.
That means Barty could be set to lose points this week as she won Miami in 2019 so is still able to count the points against her ranking.
Osaka would need to at least reach the final to overtake Barty at the top. However, if Barty reaches the semi-finals then Osaka would need to win the tournament, and if Barty reaches the final then she will keep hold of the No 1 ranking, no matter how Osaka fares.
Osaka has held the No 1 ranking for 25 weeks in total, becoming the first Japanese No 1 after winning the Australian Open in 2019. Barty took top spot in the summer of 2019 after winning titles at Roland-Garros and Birmingham, and then reclaimed it in September after Osaka had another brief spell at the top.

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Barty and Osaka are the top two seeds at the Miami Open and could only meet in the final.
Speaking before the Australian Open last month, Osaka said that she is not "chasing" the No 1 ranking as she might have done in the past.
"It doesn't bother me as much as it used to," the 23-year-old said.
"I remember when I first got to No 1, I think nobody really acknowledged me as No 1. I just kept trying to prove myself and I felt that wasn't really a great mindset to have. I feel like right now I'm at a really good place. I just want to play every match as hard as I can and if it comes to the point where I'm able to be No 1 again, I'll embrace it. But, I'm not really chasing it like that anymore."
Osaka faces 16th seed Elise Mertens or 22nd seed Anett Kontaveit in the last 16 of the Miami Open while Barty has a tricky clash against two-time Grand Slam champion Victoria Azarenka.
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