Sinner, who went into Cologne at his previous career-high of No. 46, rose to No. 43 after reaching the semifinals of the ATP 250 event, falling to No. 7 Alexander Zverev in a tight two-setter. It was the second tour-level semifinal of his career, having reached the final four in Antwerp last year.
The 19-year-old Italian is the only teenager in the Top 100 of the ATP rankings.
Meanwhile, Gauff rose from No. 55 to No. 47, surpassing her previous high of No. 49, which she had set in February. The American qualified and reached the second round in Ostrava, where she narrowly lost to No. 12 Aryna Sabalenka, 1-6, 7-5, 7-6 (2), after being up a double break at 5-2 in the third set.
Sabalenka went on to win the title and inch up one spot to No. 11.
“She’s a great player, she’s so young and moving really, really well,” Sabalenka said of Gauff. “It’s long rallies all the time and it’s not easy to make a winner or find a way of finishing the point against her.
“She’s great. She’s 16 and playing on this level. I would’ve liked to be on this level when I was 16!”
Gauff is the youngest player in the Top 400 of the WTA rankings.
“I just need to play a little bit smarter on pressure points, to make my opponent play,” Gauff said after the match. “I wasn’t nervous today, I think I just need to be smarter. Sometimes I have tendencies—when it gets to the end—to rush out of the points, when instead I should put the ball in the court.”
There were a few more notable movers a little further up the rankings, including Jennifer Brady. The US Open semifinalist rose from No. 26 to No. 24—just surpassing her previous career-high of No. 25—after advancing to the semifinals of Ostrava, where she fell to Sabalenka in straight sets, 6-4, 6-4.
Brady also hopped over now-No. 26 Alison Riske to become the No. 4-ranked American woman, now trailing only No. 4 Sofia Kenin, No. 10 Serena Williams and No. 16 Madison Keys.
And 22-year-old Frenchman Ugo Humbert continued his climb up the ATP rankings, jumping from No. 38 to No. 32 after winning his second ATP title of the year in Antwerp. His first career triumph came in January at Auckland.
This week coming up could also see significant movement in the race to the ATP Finals. Six players—Novak Djokovic, Rafael Nadal, Dominic Thiem, Stefanos Tsitsipas, Daniil Medvedev and Zverev—have already qualified. Four of the five leading contenders for the last two spots are all playing at the 500-level event in Vienna: Andrey Rublev, Diego Schwartzman, Gael Monfils and Denis Shapovalov.