(Reuters) - Bulgarian Grigor Dimitrov broke the third-round barrier at Roland Garros for the first time this week but knows he will need to find another gear when he takes on fifth seed Stefanos Tsitsipas on Monday. Dimitrov grew up competing on claycourts across Europe but struggled to explain why he had to wait until his 10th French Open appearance to secure a last-16 spot. “I wish I could explain why this year,” Dimitrov, seeded 18th, told reporters. “I’m not the one to make excuses, but I’ve always had players that were just getting the best out of me. Especially in the third rounds.” This will be Dimitrov’s first meeting with world number six Tsitsipas, who completed his transition from hardcourts to clay by reaching the Hamburg Open final last month. “I don’t know much about him, to be honest, outside the court,” Dimitrov said. “I’ve watched him play a lot of matches. He’s been having very, very good results, playing good tennis on any surface. “I’m excited first of all to be in the second week of the tournament. I want to hold onto it and kind of focus on my side of the net.” In other matches on Monday, world number one Novak Djokovic will continue his pursuit of an 18th Grand Slam title when he meets Russian Karen Khachanov while Spain’s Pablo Carreno Busta goes up against German qualifier Daniel Altmaier. Australian Open champion Sofia Kenin is bidding to reach her maiden quarter-final in Paris against local hope Fiona Ferro. Tunisia’s Ons Jabeur, the first Arab woman to reach the fourth round at Roland Garros, will look to continue her dream run against American Danielle Collins.