Grigor Dimitrov reached the second round of the Rotterdam World Tennis Tournament with a 6-7 (4-7), 6-2, 6-4 win over Mischa Zverev Wednesday as the red-hot Bulgarian racked up his 15th win of 2017. Dimitrov, who captured his second title of the season last weekend on home ground in Sofia, had to dig deep, however, to see off Zverev who stunned world No. 1 Andy Murray at the Australian Open last month. The 25-year-old Dimitrov improved to 15-1 on the season and will next face Denis Istomin, who beat Novak Djokovic in the second round in Melbourne at the season's opening Grand Slam. Dimitrov, the fifth seed, took victory in just under two hours, firing his 11th ace for a match point and breaking on four of nine occasions. "I'm pleased with the win. Mischa did not make it easy for me with his game. I had to fight to win," said Dimitrov, who was champion in Brisbane and a semifinalist at the Australian Open in January. Belgian third seed David Goffin comfortably beat Andrey Kuznetsov 6-3, 6-2 Richard Gasquet put out Viktor Troicki 6-4, 6-2, ending with a pair of picture-perfect backhand passing shots. In the second round, defending champion Martin Klizan battled to a 6-7 (5/7), 6-4, 6-1 defeat of 2016 semifinalist Philipp Kohlschreiber. Frenchman Pierre-Hughes Herbert advanced past qualifier Evgeny Donskoy of Russia 6-2, 7-6 (7/4). Top seed Marin Cilic battled past temperamental French opponent Benoit Paire 5-7, 6-3, 6-2 for only his second win of the year Tuesday. Cilic, a 2014 finalist, struggled with an out-of-sorts and injured Paire, whose racket-smashing antics left him flirting with the wrath of the chair umpire in a match lasting more than two hours. Sixth-seeded Frenchman Jo-Wilfried Tsonga was kept guessing by unheralded Greek Stefanos Tsitsipas before grinding out a 6-4, 7-6 (7/2) first-round win. In round two Tsonga faces Sydney champion Gilles Muller after the Luxembourg veteran beat Dutchman Tallon Griekspoor 6-3, 6-2 with 14 aces as the number 317 youngster made his ATP main draw debut. Holder Martin Klizan of Slovakia began his title defence with a defeat of Fernando Verdasco 6-4, 0-6, 6-1 while last year's semifinalist Philipp Kohlschreiber took out eighth seed Lucas Pouille of France 7-5, 6-2. Frenchman Gilles Simon overcame compatriot Nicolas Mahut 3-6, 6-3, 6-4. King upsets Tomic Darian King of Barbados won his opening match at the Memphis Open Tuesday, surprising fifth seeded Bernard Tomic 6-4, 6-4 in the first meeting between the 24-year-olds. King, who had to go through the qualifying rounds to get into the tournament, is making just his second appearance in the main draw of an ATP Tour event. He hammered four aces, won 75 percent of his second-serve points and had no double faults in the 66-minute match. In other first round matches Tuesday, Tomic's fellow Aussie Matthew Ebden rallied to beat Canadian qualifier Peter Polansky 6-7 (4/7), 6-3, 6-1 and American Ryan Harrison eased past Russian Konstantin Kravchuk 6-3, 7-5.