World number one Aryna Sabalenka and number three Coco Gauff have both been knocked out in the second round of the Qatar Open.
Sabalenka was beaten by Ekaterina Alexandrova at the WTA 1,000 event in Doha, while Gauff lost to Marta Kostyuk.
Russian Alexandrova, who beat Emma Raducanu in the first round, came from a break down twice in the third set and held serve twice against three-time Grand Slam champion Sabalenka.
The world number 26 then held her nerve in the third set tie-break to secure a 3-6 6-3 7-6 win.
The 30-year-old, who won a WTA Tour title in Austria last week, will play Belgium’s Elise Mertens in the last 16.
Ukrainian Kostyuk, the world number 21, fought back from 3-1 down in the second set to wrap up a 6-2 7-5 victory over Gauff in just 73 minutes.
It is a second successive defeat for Gauff, who received a bye in the first round and was playing for the first time since she lost to Paula Badosa in the quarter-finals of the Australian Open last month.
The 2023 US Open champion was undone by seven double faults and 39 unforced errors while she managed just eight winners.
Gauff had won her last 17 matches against opponents ranked outside the top 20 before facing Kostyuk.
The 22-year-old will now face the winner of an all-Polish tie between Magda Linette and Magdalena Frech.
Elsewhere, former Wimbledon champion Elena Rybakina claimed a 6-2 6-4 win against American Peyton Stearns, while Jasmine Paolini – last year’s Wimbledon and French Open runner-up – defeated Caroline Garcia 6-3 6-4.
Three-time Grand Slam finalist Ons Jabeur set up a meeting with former Australian Open champion Sofia Kenin after beating world number eight Qinwen Zheng of China 6-4 6-2.
It was the Tunisian’s first win against a top-10 opponent since last year’s Madrid Open after struggling with injury.
Slovakia’s Rebecca Sramkova fought back from a set down to beat 12th seed Mirra Andreeva 3-6 6-3 7-5, while American sixth seed Jessica Pegula beat Elina Svitolina 6-3, 7-6 (7-3).
Linda Noskova won 6-2 6-3 against Kazakhstan’s Yulia Putintseva to set up a last-16 meeting with three-time defending champion Iga Swiatek.
