The 14th-ranked Dimitrov, a Bulgarian who at 22 is the youngest player in the top 20, did not take well to the red-and-white towels at the Foro Italico.
"They're new and they don't absorb any sweat," he said. "Three or four times I was about to lose my racket. I asked several times (for all-white towels) but they told me, `We don't have it."
Dimitrov will next face big-serving Ivo Karlovic, who beat Spanish qualifier Pablo Carreno Busta 3-6, 6-3, 7-6 (4).
In an upset, 13th-seeded Fabio Fognini, the top Italian hope, was handily beaten by 56th-ranked Lukas Rosol of the Czech Republic 6-3, 6-2.
In women's play, 11th-seeded Ana Ivanovic defeated Italian wild-card entry Karin Knapp 6-1, 6-1, 1999 champion Venus Williams cruised past Annika Beck of Germany 6-3, 6-1, local favorite Francesca Schiavone of Italy eliminated 17th-seeded Eugenie Bouchard 6-4, 6-2, and Svetlana Kuznetsova ousted fellow Russian Maria Kirilenko 7-5, 6-0.
The eight top-seeded players have first-round byes.
Second-ranked Novak Djokovic is back after withdrawing from last week's Madrid Open with a right wrist injury and Roger Federer was out on the practice courts after also taking last week off to welcome the birth of his second set of twins.
Top-ranked and defending champion Serena Williams, however, wouldn't commit to playing as she waits to see how her injured left thigh feels.
"I'm taking it a day at a time. We'll see as the week goes on. I have the rest of the day off and I'll see how I feel tomorrow," Serena said. "I hit some balls today a little bit so I'm going to see later tonight how it feels."
Serena withdrew before her quarterfinal match in Madrid, where she had her thigh heavily bandaged and said the injury occurred during a first-round victory over Belinda Bencic.
One of the only top players not in Rome was Kei Nishikori of Japan, who retired midway through Sunday's Madrid final against Rafael Nadal citing a lower back and hip injury.
Rome is the last key clay-court warmup before the French Open starts in two weeks.