German qualifier Jan-Lennard Struff upset fourth-seeded Casper Ruud 6-1, 7-6 (8-6) to reach the quarter-finals of the Monte Carlo Masters on Thursday. Ranked 29th in the world, Struff dropped as low as No 168 after sustaining a foot fracture last year in Miami, an injury that left him sidelined for more than two months. Struff has enjoyed a good start to the season and returned to the top 100 last month but had not beaten anyone in the top 10 since June 2021. On Thursday, his aggressive style of play resulted in 37 winners and 23 points won at the net against Ruud, who dropped his serve four times and saw his nine-match winning streak on clay come to an end. The 2022 French Open runner-up had won his past two tournaments on the surface, in Gstaad last July and in Estoril last week. Struff will next be up against 2021 runner-up Andrey Rublev, who beat Karen Khachanov 7-6 (7-4), 6-2. “We know each other too well," Rublev said. "The first set was only mental. We didn’t show some tennis skills. But it was tough to show skills because the wind was really hard and the court was slippery and it was tough to do something.” Meanwhile, Jannik Sinner was made to toil by Hubert Hurkacz as the Italian seventh seed saved a match point to seal a 3-6, 7-6 (8-6), 6-1 victory and book his spot in the last eight. Watched on by sprint great Usain Bolt in the stands, Hurkacz raced to a 3-0 lead before Sinner got on the board and the world No 13 wobbled towards the end of the opening set before wrapping it up with two fiery first serves. Sinner, a Monaco quarter-finalist last year as well, found himself in more hot water shortly after the second set began but the 21-year-old hit back after dropping serve to grab a break and level at 2-2. Hurkacz raised his game to force a tiebreak and looked in control but the scrappy Sinner saved a match point and dragged the contest into a decider. The Italian then got his nose in front and held firm to complete the win as Hurkacz faded. “Playing against him, I knew already from the beginning that it was very tough to get into the rhythm," Sinner said. “I think he served incredible in the first one and a half sets, and when I broke him the first time the momentum changed a little bit.” Sixth-seeded Holger Rune advanced to the quarter-finals without playing when Matteo Berrettini withdrew due to an injury