The 19-year-old Tomic, based in Monte Carlo, dominated the Spaniard, whose movement was hampered by a left foot injury. After the first set he sought courtside treatment for his right foot.
"It was not easy," Tomic said. "He is a good player and won this tournament before. But I'm playing really well. I'm happy that I arrived here early and trained under the heat to get ready. I have to keep my head up."
Former finalists Viktor Troicki of Serbia and Jarkko Nieminen of Finland also won.
Troicki, runner-up in 2009, beat Sergiy Stakhovsky of Ukraine 6-7 (4), 7-5, 6-3, letting slip being up by a break in each set. He was also breaking in new rackets he received 10 days ago.
Nieminen, the finalist two years ago, advanced while leading 6-1 against Japanese qualifier Yuichi Sugita, who retired with an ankle injury.
The fifth-seeded Fernando Verdasco of Spain beat Tatsuma Ito of Japan 3-6, 6-0, 6-2, taking a while on the indoor hard-courts to gauge his first-time opponent.
"It's always difficult to play someone you have never seen before," Verdasco said. "I was surprised. In the end I was physically better."
Japanese qualifier Hiroki Moriya earned his first win on the tour this year when he beat Robin Haase of the Netherlands 2-6, 7-6 (6), 6-3, and Dudi Sela of Israel downed Marco Chiudinelli of Switzerland 6-4, 6-4.