The only seeded players in action on the opening day, No. 7 Montanes served eight aces in defeating Adrian Ungur 6-4, 6-2, and No. 8 Granollers beat Mate Pavic 7-6 (2), 6-2.
Granollers, who saved all six break points against his serve, will next play Horacio Zeballos, who beat Martin Fischer 7-5, 1-6, 6-3.
Also, Leonardo Mayer defeated Kenny De Schepper 6-4, 6-4 to set up a second-round match against top-seeded Philipp Kohlschreiber. The top four seeds have a bye in the opening round.
Dominic Thiem rallied from 4-1 down in the second set to beat Andrey Kuznetsov 6-2, 7-5. It was the first ATP match this season for the 268th-ranked Thiem because of a viral illness. He will play fourth-seeded Jurgen Melzer in an all-Austrian clash.
Daniel Gimeno-Traver conceded only nine points on serve in routing Antonio Veic 6-1, 6-3.