The French Open and U.S. Open champion has won five titles this season and is closing in on the year-end No. 1 ranking.
"In general terms, I think I played with not many mistakes," Nadal said. "I don't remember a lot of mistakes. I went to the net very often. I think I did the things that I want to do, and I did it well, so very happy."
Dimitrov spent time practicing with Nadal in Mallorca ahead of the hard-court season. The two also spent time fishing.
"We went out with the boat," Nadal said. "We catch a few ones (fish), but not very big. But we had some good dinner."
Earlier, second-seeded Simona Halep reached the semifinals by beating Daria Kasatkina 6-2, 6-1.
The Romanian could take over the top ranking from Garbine Muguruza. She needs to reach the final and not lose to third-seeded Elena Svitolina.
Halep will next face either ninth-seeded Jelena Ostapenko or Sorana Cirstea.