AP Photo/Kirsty WigginsworthIt took less than 24 hours for the 2021 Wimbledon Championships to see the first major upset.Stefanos Tiafoe, who reached his first Grand Slam final two weeks ago, was shocked to lose in straight sets to Stefanos Tsitsipas in the All England Club's opening-day action.Tsitsipas' shocking loss is the headline of the day. This was on a day where Sloane Stephens defeated Petra Kvitova, and Andy Murray returned to the court with an upset victory over Nikoloz Basilashvili.2021 Wimbledon Results – MondayMen's singles(1) Novak Djokovic Def. Jack Draper 6-1, 6-2.Frances Tiaoe Def. (3) Stefanos Tsitsipas, 6-4, 3-3, 6-3(5) Andrey Rublev def. Federico Delbonis, 4-6,6-4, 6-2 and 6-1(8) Roberto Bautista Agut Def. John Millman 6-2.3-6.6-3.7-6(18) Elena Rybakina Def. Kristina Molevic 6-4, 6Marton Fucsovics Def. (19) Jannik Siner 5-7. 6-3. 7-5. 6-3Andy Murray wins. (24) Nikoloz Basilashvili, 6-4, 3-3, 5-7, 6-3(25) Karen Khachanov def. Mackenzie McDonald's 3-6, 6-3 and 6-4, 7-6 (3)Denis Kudla def. (30) Alejandro Davidovich Fokina, 5-7, 6-8, 7-6 (4). 6-3.Singles for Women(2) Aryna Sabalenka def. Monica Niculescu 6-1, 6-4(4) Sofia Kenin def. Wang Xinyu 6-4.(7) Iga Swaiatek def. HsiehSuwei 6-4.Sloane Stephens defeat. (10) Petra Kvitova, 6-3, and 6-4(11) Garbine Mguruza def. Fiona Ferro 6-1, 6-0(23) Madison Keys win. Katie Swan 6-3 and 6-4Viktorija Golubic wins. (29) Veronika Kdermetova 3-6.(32) Ekaterina Alexova def. Laura Siegemund 6-1.Tsitsipas chose to not play on grass courts this month, in preparation for Wimbledon. His failure to convert break opportunities was a major reason why he lost. Tsitsipas missed seven of his chances, while Tiafoe won four. This was enough to make it through the razor-thin margin."It was clear that today's matches were crucial. I believe the transition from clay to grass is the most difficult, if certainly the greatest challenge, in our sport. Tsitsipas stated that he was unable to adapt. "It was not what I wanted, and it is getting out of control."I didn't have the same fighting spirit on the court as I used to. I would love to see a new me next time. Sometimes I have been more motivated than that. I don't think that should stop me from playing well."Tiafoe was best at Wimbledon in 2018's third round. Since his Australian Open quarterfinals run in 2019, Tiafoe has not reached the fourth round of Grand Slam.Novak Djokovic defeated Jack Draper in four sets to become Tsitsipas' French Open counterpart. With his third consecutive Wimbledon title, Djokovic is tied with Roger Federer and Rafael Nadal for the most Grand Slams of men's tennis.After a run to fourth round at the French Open, Stephens continued her impressive streak of play with straight-sets victory over Kvitova. Although she has not reached the third round of Wimbledon, the 28-year old expressed her confidence after defeating Kvitova, the two-time champion.Stephens stated, "Not playing on grass in two years, and being able come back first match and take part on Centre Court is really just an dream." "I am just excited to compete."I love grass. It just doesn't translate. It has been several years since I have had any good results on grass. This is a great start. I beat a very good grass-court player. I hope to have a good run.Madison Keys and Sofia Kenin, both Americans, were victorious in straight sets victories.Murray, who was playing at Wimbledon for the first time since 2017, looked impressive in winning four sets against Nikoloz Basilashvili. Since his injury-related hiatus, Murray has never reached the second round of a major. Fans were treated to a wild celebration after his victory, with many matches being suspended due to darkness.