Mumbai, May 29 -- There were many moments when Jannik Sinner looked like he was about to throw his racquet in frustration. And many more when his racquet did not make a sweet connection. In the first point of the fifth set, Sinner - a player who clings to the baseline - floated up to the net to try and serve-and-volley. He has done that a few times in his career, but on Thursday, under a blazing Parisian sun, the tactic came out of desperation. His legs had given up, and he was trying everything he could to keep the points short. At the other end, Juan Manuel Cerundolo spotted Sinner's charge up the court. The return was an attempted lob that was a touch deeper than the Italian would have liked. Sinner backpedalled a step, and then his attempted smash caught the frame of his racquet. It set the tone for the biggest upset at the French Open this year, with the world No.56 from Argentina beating top seed Sinner 3-6, 2-6, 7-5, 6-1, 6-1 in a second round match that lasted three hours and nine minutes. For a majority of that time though, Sinner was in control. The four-time Grand Slam champion was up two sets and leading 5-1 in the third. Then the heatwave in Paris got the better of him. He had to go off court for treatment, but was a pale shadow of himself when he returned. In the last 20 games of the match, Cerundolo won 18 to secure passage into Round 3. "It's tough for him. He (played so well) I could not win more than three games (in the first two sets)," Cerundolo said. "I was a little bit lucky. I feel sorry for him. He deserved to win." The heat in Paris has been a major talking point in the first few days of Roland Garros as the French capital falls under a "heat dome" - when the warm air from North Africa is trapped over western Europe under a high-pressure system, according to the BBC. Incidentally, Sinner's clash was scheduled as the opening fixture on Court Philippe-Chatrier for Thursday's matches to help him avoid playing in the hottest part of the day. However, despite the heat, the Grand Slam's heat policy has still not come into effect. The French Open has two wet-bulb sensors in the complex, which takes into account temperature, humidity, radiation and ventilation. Should the sensor touch 32.2 degrees, play is suspended....