PARIS — Jannik Sinner’s bid for a career Grand Slam wilted at the French Open Thursday afternoon, as he lost in the second round having been four points from victory.The world No. 1 came into the match off the back of 30 straight wins, but lost 3-6, 2-6, 7-5, 6-1, 6-1 after succumbing to his kryptonite: Heat. Sinner’s defeat, to Argentina’s world No. 56 Juan Manuel Cerúndolo, was a seismic shock. How it played out was entirely predictable.From the start of the tournament, the biggest threat to Sinner appeared not to be any of the other 127 players in the draw, but the conditions.Melbourne’s hot weather nearly helped to knock Sinner out of January’s Australian Open. In high temperatures and humidity at October’s Shanghai Masters, full-body cramps forced him to retire against Tallon Griekspoor, accounting for his last defeat at ATP Masters 1000 level, the rung below the Grand Slams.Unlike in Melbourne, when the Australian Open’s heat rule saw the roof close just as Sinner was on the brink, there was no reprieve in Paris.With temperatures at around 90 degrees and no shelter on Court Philippe-Chatrier, Sinner was pushed to the point of near-collapse.The dramatic scenes felt impossible toward the end of the third set, when Sinner appeared to be in complete control. He led 6-3, 6-2, 5-2, and was serving for the match, but then suffered a spectacular collapse. A game away from victory, Sinner completely faded in the afternoon heat and lost 18 points in a row.