Dimitrov, the 26th seed, will be playing in the last 32 of a major for the first time after breezing past French wildcard Lucas Pouille, the world No 324, in straight sets 6-1, 7-6 (7-4), 6-1.
Djokovic lost to Dimitrov in the Madrid Masters second round early last month.
"Even though his style of game could be better on the hard court or faster surfaces, he's showing that he can play equally well on clay," said Djokovic.
"Here it's best of five. It's going to be very physical and all the hard work that I put into preparations for this tournament hopefully will play to my advantage and will pay off on the court."
Chinese star Li went down 5-7, 6-3, 6-2 to brash American Bethanie Mattek-Sands in what was the 31-year-old's earliest defeat at the tournament in seven appearances.
- AAP