Defending champion Marketa Vondrousova crashed out of Wimbledon in the first round on Tuesday in London.
The 25-year-old Czech fell 6-4, 6-2 to Spain's Jessica Bouzas Maneiro at Centre Court.
The last time a reigning champ lost in the opening round at the All England Club was in 1994, when Steffi Graf fell to Lori McNeil.
Vondrousova made history last year as Wimbledon's first unseeded female champion when she captured her first Grand Slam title with a 6-4, 6-4 win over Tunisia's Ons Jabeur.
Seeded sixth this year, Vondrousova showed some after-effects of a recent hip injury during Tuesday's shocking loss to Bouzas Maneiro, 21.
"This is one of the most important moments in my life, in my career, here in this sport. This is amazing," said Bouzas Maneiro, who is ranked 83rd this week, equaling her career high.
"I was like, 'I have no pressure, just enjoy the moment, enjoy the tournament.' Just trying to be free playing, and I did it, so I'm happy for that," she said.
Vondrousova double-faulted seven times and Bouzas Maneiro converted all five of her break chances in the 69-minute match. Vondrousova committed 28 unforced errors, twice as many as her opponent.
No. 1 seed Iga Swiatek of Poland had no trouble in her opener, defeating Sofia Kenin 6-3, 6-4 in 79 minutes. Swiatek has won 20 consecutive matches – including titles in Madrid, Rome and Paris – and 44 matches in 2024 to lead all WTA players.
"Honestly, on (grass) it's not about the result for me, (or) about the progress in terms of if I'm doing things better than last year, " said Swiatek, who has never been past the Wimbledon quarterfinals. "I'm not really looking at numbers or statistics, just trying to be better every day."
Also winning in straight sets were No. 4 Elena Rybakina of Kazakhstan and No. 5 Jessica Pegula. Rybakina ousted Elena-Gabriela Ruse of Romania 6-3, 6-1, while Pegula defeated fellow American Ashlyn Krueger 6-2, 6-0 behind five aces and five service breaks.
Other seeded players to advance Tuesday were No. 10 Jabeur, No. 13 Jelena Ostapenko of Latvia, No. 15 Liudmila Samsonova of Russia, No. 17 Anna Kalinskaya of Russia, No. 23 Caroline Garcia of France, No. 27 Katerina Siniakova of the Czech Republic, No. 30 Leylah Fernandez of Canada and No. 32 Katie Boulter of Great Britain, a home-court favorite.
Former World No. 1 Caroline Wozniacki of Denmark needed just 53 minutes to defeat American Alycia Parks 6-2, 6-0. But fellow American Robin Montgomery, 19, beat Olivia Gadecki of Australia 6-4, 6-4 in her Wimbledon debut.
The final match of the day was suspended due to darkness with No. 11 seed Danielle Collins leading Denmark's Clara Tauson 6-3, 4-4.