Swiss Bencic will face American Sofia Kenin who earlier did what no other player has done at the event by stopping Latvian Anastasija Sevastova reaching the final with a 6-4 4-6 6-2 win.
"This means a lot to me," Bencic said. "I fought very hard today. She was playing great tennis and the balls were keeping very low. Tomorrow I can just play freely and enjoy it."
Second seed Sevastova had reached all three previous finals at the tournament that became part of the WTA calendar in 2016 -- winning the title once.
But 20-year-old Kenin, who reached the last 16 at the French Open this month, ended that run as she stepped up a gear in the deciding set to storm to victory and inflict only a third loss in 19 matches for Sevastova on the Santa Ponsa lawns.
Kenin has gone one stage further than last year when she reached the semi-finals as a qualifier.
(Reporting by Martyn Herman, editing by Pritha Sarkar and Tony Lawrence)
