Third seed Andrey Rublev suffered a first round exit after his Qatar Open title, losing to qualifier Quentin Halys 3-6, 6-4, 7-6(5) at the Dubai Tennis Championships on Tuesday.
For the 77th-ranked Halys, who next faces Roberto Bautista Agut, it was his first victory over a top-10 opponent.
"At the moment, it's a bit hard to comprehend," the 28-year-old Frenchman said.
"Mentally, it was a very difficult match. Andrey is maybe tired from his week in Doha. Beating a top-10 (opponent) is a significant moment in your career. I'm happy it happened today."
The ninth-ranked Rublev won the Dubai title in 2022 on Saturday, beating Jack Draper in the final.
Meanwhile, top-seeded Daniil Medvedev beat Jan-Lennard Struff 6-4, 7-6 (4) and will next face Giovanni Mpetshi Perricard.
Second-seeded Alex de Minaur lost to 2014 US Open champion Marin Cilic 6-2, 3-6, 6-3 and Nuno Borges eliminated eighth-seeded Arthur Fils 6-2, 6-1.
Other winners on Tuesday included fifth-seeded Ugo Humbert, Matteo Berrettini, Felix Auger-Aliassime and qualifier Christopher O'Connell.
Zverev fights back to overcome Arnaldi
Top seed Alexander Zverev, who won the event in 2021, rallied from a first-set loss to down Matteo Arnaldi 6-7(2), 6-3, 6-4 in the second round of the Mexican Open, in Acapulco.
Germany's Zverev, ranked No. 2 in the world, converted two of four break-point opportunities and saved all three break-points to work past Italy's Arnaldi, ranked No. 33, in two hours, 44 minutes.
Denmark's Holger Rune, the fourth seed, eliminated Spain's Roberto Carballes Baena 7-6(4), 6-3.
Ninth-seeded Denis Shapovalov of Canada won in straight sets over American qualifier Nishesh Basavareddy 7-5, 6-2.
Unseeded winners were Spain's Alejandro Davidovich Fokina, Brandon Nakashima and Mexican wild-card Rodrigo Pacheco Mendez.
Seventh-seeded Frances Tiafoe defeated France's Alexandre Muller 6-4, 6-2 in the late match.
Krejcikova out of Indian Wells with back issue
Wimbledon champion Barbora Krejcikova has withdrawn from next month's tournaments at Indian Wells and Miami due to a back injury that has kept her out of action since November.
The world number 16, a surprise champion at the All England Club last year, sustained the injury during the Tour's Asian swing of tournaments and appeared hampered by it at the WTA Finals in Riyadh, where she reached the semi-finals.
The 29-year-old Czech skipped the Australian Open Grand Slam in January, saying she needed more time for her injury to heal.
Austria's Julia Grabher will take Krejcikova's place in the main draw at Indian Wells, which begins on March 5, organisers said.
The Miami tournament kicks off on March 18.
Saville upsets Kostyuk at Merida Open
Daria Saville of Australia converted 6 of 10 break points to upset No. 6 seed Marta Kostyuk of Ukraine 6-4, 7-6 (6) in first-round action in Merida, Mexico.
aville rallied out of a 3-0 deficit early in the second set as well as a 2-0 hole to start the ensuing tiebreaker. She saved one set point at 6-5 on her way to winning the final three points of the match, taking down the 19th-ranked player in the world.
Croatia's Petra Martic swept past Sloane Stephens 6-2, 6-3. Poland's Magda Linette and Slovakia's Rebecca Sramkova also won in straight sets, and Francesca Jones of Great Britain led 6-4, 3-0 when Egyptian opponent Mayar Sherif retired.
Two remaining matches pitted Greek eighth seed Maria Sakkari against Turkey's Zeynep Sonmez and Romania's Jaqueline Cristian against Ukrainian Yuliia Starodubtseva.
No. 3 seed Peyton Stearns ousted in Austin
France's Varvara Gracheva fended off 5 of 6 break points to defeat No. 3 seed Peyton Stearns 6-2, 6-3 in the Round of 32 at the ATX Open on Tuesday in Austin, Texas.
Stearns, who had six aces with six double faults, saved three match points but not a fourth in the final game of the match.
No. 1 seed Jessica Pegula led Arantxa Rus of the Netherlands 6-3, 3-2 when Rus retired due to injury. No. 2 seed Diana Shnaider eked past fellow Russian Tatiana Prozorova 0-6, 6-2, 7-5, and Great Britain's Jodie Burrage hit a career-high 14 aces to beat Petra Kvitova of the Czech Republic 3-6, 6-4, 6-4.
Other early winners included Caroline Dolehide, Germany's Tatjana Maria, Japan's Ena Shibahara, Belgium's Greet Minnen and Spaniard Cristina Bucsa. Two more matches remained Monday night: Romania's Sorana Cirstea against Germany's Laura Siegemund and Dutch eighth seed Suzan Lamens against Russia's Kamilla Rakhimova.