ATP World No. 1 Jannik Sinner is out of the 2026 French Open. The extreme heat in Paris has been a major issue for men's and women's players this week, but it just played a role in Juan Manuel Cerundolo's incredible upset victory.Cerundolo, who was also dealing with the brutally high temperatures, outlasted Sinner in five sets: 3-6, 2-6, 7-5, 6-1, 6-1. Sinner raced out to an early 2-0 lead, but began showing signs of fatigue early in the match. Eventually, Sinner needed an examination from his physio, even leaving the court during the third set to deal with cramps.No. 1 Jannik Sinner exited the court after dealing with apparent cramps. #RolandGarros pic.twitter.com/2jtqoUOf3R— TNT Sports U.S. (@TNTSportsUS) May 28, 2026By the time Sinner returned to finish the match, he was there in body only. Cerundolo rattled off 18 of 20 games, sealing the biggest win of his career. For Sinner, it will add to the growing chorus of detractors chastising his ability to play in the heatHowever, there are bigger implications and takeaways from this stunning upset. First, Sinner's dominant run of 2026 came to a crashing close on the clay court of Court Philippe-Chatrier. NO. 1 JANNIK SINNER IS OUT AT ROLAND-GARROS 😳🤯Sinner experienced cramps in his second round match with Juan Manuel Cerundolo. pic.twitter.com/UH3cWpnvyD— TNT Sports U.S. (@TNTSportsUS) May 28, 2026Secondly, with Carlos Alcaraz missing the tournament due to a wrist injury, that means to Sinner-Alcaraz showdown in the final — a new Grand Slam champion will be crowned for the first time since Novak Djokovic won the 2023 US Open. Djokovic was also the last player outside of Sinner or Alcaraz to win Roland Garros back in 2023.According to tennis reporter Reem Abuelleil, Cerundolo said after the match, "Of course it's tough for him. He was leading the match; I couldn't win more than three games by set, so I think I was a little bit lucky. I feel sorry for him because he deserves to win a lot of majors and was deserving to win in this match."Jannik Sinner loses to Juan Manuel Cerundolo after facing physical difficulties. Hope you get better soon 🧡#RolandGarros pic.twitter.com/U8qTNvl6e0— Roland-Garros (@rolandgarros) May 28, 2026Sinner's clay court season is over, and he will have a much longer than expected break before the start of the grass court season. The Italian superstar will look to defend his title at Wimbledon without Alcaraz in the draw again. Meanwhile, World No. 56 Cerundolo improves to 7-9 on the season. The Argentinian will face either Martin Landaluce or Vit Kopriva in the third round of the French Open.The French Open runs through June 7, and fans can expect more shocking results. Stay locked into Sports Illustrated's Serve On SI for all of your tennis news from the court and beyond.Add us as a preferred source on GoogleFollow