Nadal roared out to a 5-1 lead before Carreno Busta pulled back a break. Carreno Busta, who like Nadal is from Spain, then had three break chances on Nadal's next service game, but the latter saved them all and closed out the set.
Any thoughts of a Carreno Busta comeback were snuffed when Nadal broke his first service game of the second set in intimidating fashion. Carreno Busta thought he smashed the ball well beyond Nadal's reach, only for the 20-time Grand Slam winner to angle into position and blast the ball right back past him as Carreno Busta lost his footing and tumbled to the clay.
The top-seeded Nadal improved to an 8-0 career record against the 13th-ranked Carreno Busta.
"I am very happy to be back in a final here at an historic event, a home event, an important one for me," Nadal said. "I have been improving every single day a little bit more."
The second-seeded Tsitsipas advanced after beating Jannik Sinner 6-3, 6-3 for his eighth consecutive straight-set victory, including last week's title run at Monte Carlo. The Greek's 26 wins this season are matched only by Andrey Rublev on the men's circuit.
Tsitsipas beat Nadal in their past meeting in the Australian Open quarterfinals in February, when Tsitsipas rallied from a two-set deficit over four hours.
Nadal will try to stop Tsitsipas' winning streak on Sunday.
"Tomorrow will be a very tough one. (Tsitsipas) is playing probably better than ever," Nadal said. "Not one set lost in Monte Carlo and here, so it will be the toughest opponent possible. I hope to be ready."
Overall, Nadal holds a 6-2 head-to-head record with Tsitsipas, including a victory in the 2018 Barcelona Open final.
"It feels great to be back [in the final]. I will try to redeem myself from last time," Tsitsipas said.
Nadal, 34, has won all 11 finals he has reached in Barcelona. He dominated the tournament in his home country from 2005-09, 2011-13 and 2016-18. He lost in the 2019 semifinals to eventual champion Dominic Thiem. Last year the event was not held because of the coronavirus pandemic.