World No. 171 Nishioka defeated No.5 seed Verdasco despite losing the first set, coming back to win the decisive third-set tiebreak and seal a 1-6, 6-3, 7-6(5) victory.
Verdasco, who beat former world No. 1 Andy Murray in the quarterfinals, looked comfortable after winning the first set in only 29 minutes. But Nishioka fought back in the second, breaking Verdasco twice to tie the match. In the decisive third-set tiebreak, Nishioka battled from 5-4 down to secure his first-ever ATP Tour final.
There was also an upset in the earlier semifinal as Herbert defeated No. 8 seed De Minaur 7-5, 2-6, 7-6(8). World No. 67 Herbert, who will also be competing in his first ATP final on Saturday, saved two match points in the third-set tiebreak.
Frenchman Herbert also knocked out No. 2 seed Stefanos Tsitsipas earlier in the week.
Saturday's final will be the first time Herbert and Nishioka have faced each other, as the pair both seek their first career single's title.