The world number two claimed two more breaks in the next to seal the deal in an hour and 18 minutes.
But the Bulgarian, who sent down 13 aces in the match, took the fight to the Spaniard in the second set, coming from 3-0 down in a tie-break to level.
"For me, it's impossible to lose a match when I've only been broken one time", Zverev said.
Nadal, who extended his winning streak to 15 matches, pegged Dimitrov back with relentless baseline hitting to take the first set easily.
And he underlined his status as the man to beat in Shanghai as he battered the Italian Fognini 6-3, 6-1.
The Croatian, bidding to reach the season-ending ATP Finals in London, grabbed the critical break in the sixth game of the first set on his way to a comprehensive 6-3, 6-4 victory over the unseeded Spaniard.
A mouthwatering Nadal-Federer final on Sunday awaits if the celebrated pair continue at the current rate.
The talented 20-year-old Zverev was going after his sixth title of a breakthrough season and was comfortable in the first set against Argentine Del Potro, the 2009 US Open champion and 16th seed. "The game where he broke me, I was up 40-15, and I was just unfocused there".
"It's better like this than having long matches, you save, a little bit more, the body", Nadal said.
A fan at least came away with a demolished racquet for a souvenir after the young German handed it to a spectator. "We'll see tomorrow if I can have another good day". "I would like to play and be 100 per cent".
Del Potro has been suffering a left wrist injury following a heavy fall on Friday, and he may not be at his best condition. I have to try to keep focus and hold that momentum.