Defending champion Cameron Norrie lost to Argentine qualifier Mariano Navone in straight sets in the semi-finals of the ATP Rio Open.
However, the British number one struggled in Rio's hot and humid conditions.
The 22-year-old Navone, ranked 113th in the world, won 6-4, 6-2 to advance to his first ATP final.
Báez, ranked 30th in the world, will face compatriot Sebastian Báez after defeating fellow Argentine Francisco Cerundro 7-5, 6-4.
Navone and Norrie broke serve in the first two games before Navone got the decisive break in the seventh game of the first set.
They exchanged breaks again at the start of the second set, and Naborn broke Norrie again in the third and fifth games for the win.
“It's unbelievable,” Navone said. “We played very well all week. It was very hot and humid today so it was tough to play in these conditions, but we've played six games in a row so we feel pretty good.”
Thompson achieves “miraculous'' run with first tour title
Meanwhile, Australia's Jordan Thompson won in Los Cabos to claim his first career ATP title at the age of 29.
After 11 years on tour, Thompson entered the Mexico tournament with a career-high world ranking of 40th, defeating Norway's Casper Ruud in the final, beating the world No. 12 6-3, 7-6 (7-4). ) broke it.
Thompson's third Tour Finals capped a dramatic week of 12-hour play over five games.
Among them was world No. 6 Alexander Zverev, who came back from a 6-0 3-0 deficit to defeat Alex Michelsen 0-6, 7-6 (7-1), 7-5 in the quarterfinals. 7-5, 4-6, 7. -6 (7-2) in a game that lasted 3 hours and 40 minutes.
“I spent so much time on the court this week,” Thompson said. “We could have lost the double in the quarter-finals, we could have lost 6-0, 6-0. Now we're about to lift the trophy, so I think this is a miracle.”