Dominic Thiem and Grigor Dimitrov each were pushed to three sets before prevailing in the first round of the ATP's World Tennis Tournament in Rotterdam.
Thiem -- the tournament's second seed -- came back from a set down to beat rising star Alexander Zverev 3-6, 6-3, 6-4 in one hour and 44 minutes.
Zverev's brother, Mischa -- who stunned world No. 1 Andy Murray at the Australian Open -- won the first set against Dimitrov before the Bulgarian bounced back to win 6-7, 6-2, 6-4.
Third seed David Goffin had a 6-2, 6-3 triumph over Andrey Kuznetsov, and Richard Gasquet eased through to the second round with a straight-sets win over Viktor Troicki.
In the night session, Frenchmen Jo-Wilfried Tsonga booked his spot in the quarterfinals with a 6-4, 6-2 win over Gilles Muller.