Coco Gauff fought back from a set down to reach the Wimbledon semifinals for the first time after beating friend and former doubles partner Jessica Pegula 4-6 6-3 6-3 in an all-American Centre Court clash on Tuesday.The seventh seed and two-time Grand Slam winner, now the highest-ranked player left in the women’s singles draw, was on the back foot from the start against a fourth-seeded opponent who broke her in the opening game.Gauff got things under control in the second set, though she still had to survive two break points in the opening game, and halved the number of unforced errors as she fought back to break Pegula for 5-3 and hold serve.The former US and French Open winner led the match for the first time when she broke Pegula to go 2-1 up in the final set. Her opponent broke back to 3-3, but Gauff replied with another immediate break for 4-3, held serve, and then Pegula fell at the first match point.“Pretty insane, honestly” was Gauff’s immediate reaction to the win. “Considering how I hadn’t won a match on grass in two years before this tournament, I’m definitely just really happy with how I played today.”Karolina Muchova overcame four-time Grand Slam champion Naomi Osaka of Japan 7-6(4) 6-4 in an absorbing contest of athleticism, shot variety and tight margins to set up a semifinal against Gauff.The 29-year-old Czech, seeking a first Grand Slam title, proved the steadier player on a sizzling Court One, producing 21 unforced errors to Osaka’s 42 while the pair sent down 24 winners apiece.Not afraid to come to the net and volley, Muchova took the first set tiebreak with a forehand winner on her third set point.Osaka, 28 and seeded 14th, had downed top seed Aryna Sabalenka in the fourth round. But consistency deserted her as she served two double faults alongside two aces in the ninth game of the second set and missed a drive volley to drop her serve.Tenth seed Muchova served out the set, finishing with an ace, to reach her first Wimbledon semifinal.In the men’s draw, defending champion Jannik Sinner ended one of the feel-good stories at this year’s Wimbledon when he tamed big-serving German warrior Jan-Lennard Struff 7-5 7-6(4) 6-3 to reach the semifinals.In his 47th Grand Slam appearance, Struff had become the oldest man in the professional era to reach his first major quarterfinal, at the age of 36.Any hopes the world number 74 might have harboured of extending that run were snuffed out in brutal fashion by the Italian top seed.Struff had served 100 thunderbolt aces to reach the quarterfinals and fired down 12 more missiles on Tuesday, but all that firepower did little to throw Sinner off his stride.A break for a 6-5 lead in the first set was enough for the Italian to bag the set and when Struff held set point in the 10th game of the second, Sinner maintained his laser focus to produce an unreturnable serve.Danger over and Sinner, who has failed to add to his Grand Slam tally since his triumph at the All England Club 12 months ago, steamed through the tiebreak before reaching his 10th major semifinal when Struff banged a service return long.He will face either Novak Djokovic or Felix Auger-Aliassime for a place in the final. Alexander Zverev worked a longer shift than he would have hoped for in the fierce heat as he returned to Centre Court to complete his fourth-round win over Jiri Lehecka and reach the Wimbledon quarters for the first time.The German second seed had gone to bed the previous evening tantalisingly close to breaking new ground at Wimbledon, leading by two sets and 3-3 in the third under the roof when Wimbledon’s strict 11 pm curfew halted his progress.On the resumption, a listless-looking Zverev lost 12 of the first 13 points to drop the third set as Lehecka came out swinging but managed to refocus to win 6-4 7-5 3-6 7-6(6).