Defending champion Marin Cilic and unseeded Roberta Vinci were the first through to the semi-finals of the US Open on Tuesday, and both needed to go the distance against tough French resistance. With Serena Williams and sister Venus and a host of A-list celebrities waiting in the wings along with a prime time television audience for their marquee semi-final, Cilic and Jo-Wilfried Tsonga kept everything on hold as the ninth-seeded Croat battled his way to a 6-4, 6-4, 3-6, 6-7(3) 6-4 win over the scrappy Frenchman. Earlier, Italian Vinci needed a similar gritty effort to see off another player from France, Kristina Mladenovic, 6-3, 5-7, 6-4 on another sizzling hot day at Flushing Meadows. Cilic squandered three match points in the fourth set but came up strong in the fifth to stretch his Flushing Meadows win streak to 12 matches. Tsonga saved two match points in the 10th game before holding for 5-5, and another in the 12th game to force a tiebreak that he won 7-3 to set up the climactic fifth set. Cilic fought back in the final set to break Tsonga at love for a 3-2 lead and served out the set, cashing in his fifth match point in a match that stretched for four hours. "It was a big mental fight, especially after losing that fourth set," said Cilic, who will await the winner between top seed Novak Djokovic of Serbia or Spaniard Feliciano Lopez who meet later today. "Physically, it was very demanding." Demanding, yes, but nearly as hot as the conditions faced by Vinci and Mladenovic who played the opening match of the day on a baking Arthur Ashe Stadium court. The 32-year-old Vinci showed off her fighting spirit while Mladenovic, a decade younger, wilted in the punishing conditions using up all of her medical timeouts during the two-hour, 32-minute test. A doubles specialist with a career grand slam on her resume, Vinci finally cracked the solo code to move onto the final four in singles at a major for the first time in her 18-year career. "It’s an amazing moment for me. Unbelievable," beamed 43rd-ranked Vinci. "My first semi-final in my career. "It was an incredible match, so tight. But I fight a lot. At the end probably we both were a little bit tired and scared about the match but I’m so happy." Vinci, well-rested after receiving a walkover into the quarter-finals when Canadian Eugenie Bouchard was forced out of the tournament with a concussion, was pushed but never panicked against the young Frenchwoman. After splitting the opening two sets the turning point of the match came at 3-3 in the third, when Mladenovic double-faulted twice to hand Vinci a break chance and the Italian gratefully converted to take charge. "It’s not easy to play with your sister, and Serena has a lot of pressure, I think," said Vinci. "I’m so happy to be in the semi-finals so if I play Serena or Venus it doesn’t matter."