Defending champion Jannik Sinner remains on course to defend his Wimbledon crown after securing his semi-final spot following a straight-sets win over Jan-Lennard Struff on Tuesday.Without ever hitting top gear, the World No 1 was given a tough test by Struff, who was making his Grand Slam quarter-final debut, before securing a 7-5, 7-6, 6-3 victory.Sinner will now take on the winner of seven-time champion Novak Djokovic's clash with Felix Auger-Aliassime later on Tuesday for a place in Sunday's final.“He is a very, very tough player to play against but he deserves everything he's done and achieved in his career,” said four-time Grand Slam winner Sinner on court. “He's a great person off the court with an amazing team. “In the beginning, he started better than me, I was struggling a little bit. I started to serve a little bit better and tried to stay there mentally. I'm happy to be back in the semi finals here.”Since opening his title defence with a dramatic three hour, 30 minute-long victory over Miomir Kecmanovic, Sinner had secured three consecutive straight-set wins.Struff – the oldest man in the Open era, aged 36, to ⁠reach the last eight for the first time – was Sinner's fourth unseeded opponent in a row, although the German came into the game in good form having knocked out former World No 6 Hubert Hurkacz, 29th seed Brandon Nakashima and 2021 US Open champion Daniil Medvedev in the previous rounds.And Struff would stretch the World No 1 in the opener, with Sinner 5-4 down and heading into a crucial service game on the back of three unconvincing holds. But the Italian would find his range, coming through with a love-hold before making the crucial break and going on to win the set.The second would be equally tight with Sinner again not the dominating force he can be but, when it mattered most, he came through by winning the tiebreak 7-4.Struff had a mountain to climb but his staying powers could not be dismissed as three out of his four matches at the tournament so far had gone to five sets. As it turned out, the German World No 74 would run out of steam in the third as Sinner showed his class at the key moments to complete the win.In the women's draw, American seventh seed Coco Gauff came through a rollercoaster match against countrywoman Jessica Pegula over three sets on Centre Court to reach the semi-finals for the first time.The former US Open and French Open winner struggled with her timing in the opener making 17 unforced errors and four double faults, gifting Pegula an early advantage. But Gauff – whose previous three matches went to three sets – managed to regain her composure making just three double faults and 15 unforced errors across the rest of the match, as the 22-year-old came away with a 4-6, 6-3, 6-3 victory.She also becomes the seventh active player to reach the semi-finals or better at all four Grand Slam tournaments, joining esteemed company such as Venus Williams, Serena Williams, Iga Swiatek and Aryna Sabalenka.“Honestly it is pretty insane, considering I hadn't won a match on grass in two years before this tournament,” said Gauff, who will face either Naomi Osaka or Karolin Muchova for a spot in Saturday's showpiece. “I'm definitely really happy with how I played today. Jessica is an incredible opponent and person, playing against her is never easy so I'm just happy to get through this one today.“In the first set, I made a few too many errors rushing out a little bit too quickly in the rallies. But I felt like in the last two sets I played some really great tennis.“After seven years playing in this tournament, it is the first time I've walked on to Centre Court and not felt nervous. So I don't know if I'm becoming a veteran already?: