Zhuhai - Top seed Daria Kasatkina and defending champion Julia Goerges both lost to lower-ranking opponents on an afternoon for underdogs at the WTA Elite Trophy in China on Wednesday.
Kasatkina, 21, was beaten with relative ease by 23-year-old Madison Keys, who took 70 minutes to win 6-2, 6-4.
The Russian, who finished her previous match against Wang Qiang at 22:00 on Tuesday, looked tired on court and had already slammed the tournament schedule, saying it "sucks".
Keys cruised to take the first set at the Hengqin International Tennis Centre, and although Kasatkina put up a fight in the second, the sixth seed clinched the tie.
The American showed little sign of the left knee injury which forced her to retire from her last two tournaments, in Wuhan and Beijing.
Earlier Goerges suffered a bruising defeat to Anett Kontaveit.
The fifth seed took a nasty tumble mid-way through the match, which she went on to lose 2-6, 6-4, 4-6 after more than two hours.
Kontaveit, the tournament tenth seed, started brightly, breaking the world No 14 three times to take the opening set.
Goerges, 29, fell heavily on to the hard court in the sixth game of the second set, and needed to ice her right leg during the changeover.
Clearly slightly rattled, the German nevertheless dug deep to claim the set, pumping her fist and gesturing to her coach as she celebrated.
However, it was the 22-year-old Estonian Kontaveit who won the decider.
The world No 20 Kontaveit has now played both her round robin matches, after losing on Tuesday to Belgium's Elise Mertens, who will play Goerges later in the tournament. Keys will face local favourite Wang Qiang, from China.
Now in its fourth year the Elite Trophy features 12 players ranked roughly from nine to 20. This year's total prize money is $2.35 million across the singles and doubles tournaments.