Indian Wells champion Taylor Fritz ousts doubles partner Sebastian Korda MONTE CARLO: Defending champion Stefanos Tsitsipas and second seed Alexander Zverev kept their Monte Carlo Masters challenge on track with straight set wins to advance to the quarterfinals on Thursday. Tsitsipas dispatched Serbian Laslo Djere 7-5, 7-6 (7/1) with second seed Zverev easing past Spaniard Pablo Carreno Busta 6-2, 7-5 in the clay court tournament. Tsitsipas, the world No. 5, will play Diego Schwartzman for a place in the semifinal after the Argentine 12th seed rallied past Italy"s Lorenzo Musetti 2-6, 6-4, 6-3. "I had to put in a very good performance," said Tsitsipas, who lost in five sets to Novak Djokovic in the French Open final last year. "Laslo did not hand me victory, but I tried to stay 100 percent focused. "The tiebreak was pivotal and I am delighted to have produced that level of tennis," added the 23-year-old Greek. Zverev, the world No. 3, next plays Italian ninth seed Jannik Sinner who shrugged off a blistered foot to see off fifth seed Andrey Rublev, last year"s runner-up, 5-7, 6-1, 6-3. "For the second clay-court match of the season, I can"t complain too much," second seed Zverev said. "Yes, I have lost focus a little bit in the second set, but at the end of the day, he"s somebody that can really play. I"m happy with a two-set win." Zverev lost his serve immediately but converted five of his 14 break points to reach the Monte Carlo quarterfinals for the second time in his sixth appearance. "It"s great because here it"s a little bit slower I think than other clay courts that we play on, it is very important to get that confidence going on your serve," Zverev said. "All around, it"s important to get these kinds of wins." Zverev"s next opponent Sinner lost his opening service game but took hold of the tie with a winning run of six straight games in the second set despite the foot blister that forced him to retire in his Miami quarter-final flaring up. The 20-year-old received treatment in the second set to have his right toe redressed but canceled out his 43 unforced errors to 31 for his opponent with 40 winners, to 19 for Rublev. He closed out victory with a seventh break of serve after two hours and 20 minutes. Earlier, Indian Wells champion Taylor Fritz saw off his doubles partner Sebastian Korda, the conqueror of recent Miami champion Carlos Alcaraz in the previous round, 7-6 (7/4), 7-5. "It"s crazy really, I have reached the quarterfinals in four of the last five Masters tournaments," said the 13th-ranked Fritz. "If I had been luckier in Miami I could have been five from five. I am in a good place at the moment. I seem to be improving all the time." Fritz will next play Alejandro Davidovich Fokina, the Spaniard who knocked out world No. 1 Djokovic on Tuesday. Davidovich Fokina progressed to the last-eight by beating the experienced Belgian David Goffin 6-4, 6-1 on Thursday. "I carried the emotion of beating Djokovic into this match," said Davidovich Fokina. "I knew it would be a tough match as David won in Marrakech last weekend. "However, he appeared more tired than I was and I am delighted to have reached the quarterfinals." There was an upset though as Norway"s fourth-seed Casper Ruud followed Djokovic and Alcaraz out of the tournament. The Miami finalist was beaten by Grigor Dimitrov of Bulgaria, 6-3, 7-5, who next meets Poland"s Hubert Hurkacz for a place in the semifinal. Hurkacz, the 11th seed, got past Spaniard Albert Ramos Vinolas 7-6 (7/2), 6-2.