With his Indian Wells win, combined with injuries to Nadal, Djokovic and Murray, it is now looking like Del Potro is the biggest threat to Federer's rule
Simona Halep retained top spot despite her elimination in the semifinals in California.
The world No.8 is back in the top ten rankings this season for the first time since 2014.
World number 44 Osaka rolled over Kasatkina, breaking her serve four times and winning the battle of the 20-year-old rising stars in just 70 minutes.
This is the 29-year-old Argentinian will face defending champion Roger Federer in the final on Sunday
The defending champion will be aiming for a record sixth Indian Wells title
The 20-year-oldrallied to claim the biggest victory of her career and defeat seven-time Grand Slam winner.
The 26-year-old former champion Halep dropped to 18-2 on the season as she lasted just 64 minutes on the court with the unseeded Osaka.
The Canadian blasted 17 aces and broke Querrey's serve three times in the match that lasted one hour and 51 minutes
Williams is back in the semis in the California desert for the first time since pulling out before a semi-final match against Serena in 2001
Haas reached a career-high number two ranking in 2002, and finished eight seasons ranked in the top 20
In the semi-finals, Federer will face Croatian Borna Coric who outlasted seventh-seeded Kevin Anderson
The 20-year-old Russian rolled to an easy 6-0, 6-2 victory in 58 minutes over the 10th seeded Kerber at the joint WTA/ATP hardcourt tournament on Thursday.
The 26-year-old Halep improved to 18-1 on the season and is looking to win her second WTA Tour title of 2018
The world No.1 will face South Korea's Chung Hyeon in the last eight