Dimitrov raced in to unleash a backhand victor for a break point in the fourth game of the final set, but Nadal thwarted him again and claimed the decisive break to lead 4-2 before sealing yet another win.
This was their 6th meeting and the 4th win for Marin, who is yet to drop a set this week in Shanghai.
Nadal, who extended his winning streak to 15 matches, pegged Dimitrov back with relentless baseline hitting to take the first set easily.
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).
Shanghai - Rafael Nadal won his 14th match on Thursday, when it took the measure of the Italian Fabio Fognini 6-3, 6-1 to reach the quarter-finals of the Masters in Shanghai.
Cilic is close to a qualifying spot for next month's ATP Finals and will take his last two opportunities to ensure he's at the season wrap-up.
"I have a tough match against Grigor and know I will have to play my best. but I am playing well". "I like conditions also in Basel".
"I served very well today; when that happens, then the rallies are short. We'll see tomorrow if I can have another good day". The guys behind me haven't performed as well in these last few weeks. "I'm winning quite a lot of service games and a lot of matches".