American John Isner edged world No.1 Novak Djokovic 7-6 (9-7) 3-6 7-6 (7-5) in their Indian Wells Masters semi-final.
Isner fired 20 aces, including a 218-km/h bullet on his fourth match point.
Isner will play either No.2 Rafael Nadal or No.3 Roger Federer in Sunday’s final.
However, approaching rain is threatening to disrupt Saturday’s other semi-final.
The win is the 26-year-old’s first triumph over a world No.1.
Isner’s victory guaranteed he will break into the top 10 for the first time in next week’s ATP Tour rankings at No.10.
A victory in the final would move him to No.8, passing countryman Mardy Fish who is currently in that spot.
Earlier in the week Isner stopped Matthew Ebden’s impressive run at the tournament in the fourth round, beating the Australian 6-4 7-5.
Victoria Azarenka and Maria Sharapova will meet for the women’s title on Sunday.