Nadal Saturday brushed aside Dimitrov 6-2, 6-2 while Djokovic had earlier fought his way past big-serving Milos Raonic 6-7 (5-7), 7-6 (7-4), 6-3, Xinhua reported.
The Spaniard earned his first two-set win of the week as Dimitrov seemed helpless before the seven-time champion's defence.
"I think I started the match in a perfect way, in the second set he made more mistakes than usual," said Nadal.
"But, talking about myself, I played a solid match and was very good with my backhand. Yesterday (Friday) I played a great match and today (Saturday) was a good confirmation that I play better, that the forehand starts to fly again, the top spins as well. A lot of positive things," he said.
He will play against Djokovic for the 41st time, with the Spaniard leading 22-18 overall but Djokovic faring better in ATP Masters finals with a 7-4 record.
Djokovic needed three hours to get past Canadian eighth seed Raonic, who fired down 17 aces to the Serb's three.
"It's a big win because it gives me strength and belief that I can hopefully carry towards the final and the rest the season," said Djokovic, aiming for a third Rome title.