The 31-year-old is closing in on finishing the year as world No.1 for the first time since 2013.
Dimitrov took Nadal into a decider at the China Open last week only to go off the boil when it mattered most to lose the game.
The 870th career win for Nadal ties him at No 6 in the all-time Open era list behind Andre Agassi, Jimmy Connors (1,256 each), Roger Federer (1,121), Ivan Lendl (1,068), Guillermo Vilas (929) and John McEnroe (877).
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.
The Swiss tennis maestro dismantled Gasquet 7-5, 6-4 in a one-sided match that lasted more than an hour.
A mouthwatering Nadal-Federer final on Sunday awaits if the celebrated pair continue at the current rate.
Del Potro beat Federer in the U.S. Open quarterfinals.
And then came the turning point - and a flash of anger from third seed Zverev - as he yielded the crucial service break to go 3-2 down in the third set.
Fognini was playing the day after being handed a suspended ban from two grand slams and $96,000 (A$123,000) fine for verbally abusing a female umpire at the US Open.
"I'm a bit pissed off because I feel like I played well and that's the upsetting part of it - I could have done great in this tournament".
"I saw his frustration, for sure". I have to try to keep focus and hold that momentum.
"Remember when Roger (Federer) was young?"