Polish world number one PIga Swiatek made it 37 straight when 37th-ranked French Alize Cornet defeated Swiatek in the Wimbledon third round.
Since then, Swiatek has only played two tournaments, but in neither of these has she reached the semifinals.
Unexpected loss in Toronto
First, at home in Poland, it stopped in the quarter-finals against France's Caroline Garcia.
Then there was a loss to the unseeded Brazilian Beatriz Haddad Maia in the round of 16 in Toronto last week.
And late last night, 24th-ranked American Madison Keys beat Swiatek 6-3, 6-4 in the Cincinnati round of 16, winning for the first time in her career against a world number one.
In the previous five attempts there had been losses.
- It feels great.
I obviously didn't have much success against world No.1s before, so to manage to win against Iga means a lot to me, especially since I've already lost twice to her.
And I think I played pretty good tennis, says Keys on the WTA tour's website.
Saved four match points
Swiatek led 3–2 in the first set, but then Keys won ten straight games and went up 5–0 in the second set before Swiatek came alive.
But after four saved match points, she couldn't resist any longer, and Keys was able to secure the victory and advance to the quarter-finals, where she will meet Wimbledon winner Jelena Rybakina.
- I had a few games with match balls, so I'm so happy that I managed to bring it home.
The last time we met, she beat me really well, so I'm glad I got the win, says Keys, who won the tournament in 2019.
The reigning US Open champion, Emma Raducanu, is also eliminated in Cincinnati.
She lost 5–7, 4–6 against world number eight Jessica Pegula.
The last Grand Slam of the year, the US Open, begins in ten days.