US Open winner Sloane Stephens saw off three-time Miami Open winner Victoria Azarenka to book a place in the final in Florida.
The Belarusian former world No 1 was given a wildcard into the tournament and had already seen off Karolina Pliskova, Agnieszka Radwanska and Anastasija Sevastova en route to the last four.
Azarenka took the first set 6-3 in 46 minutes, after breaking Stephens twice for a 3-0 lead, but then being broken back twice for 3-3.
The 186th-ranked Azarenka broke the American twice more to seal the set.
Four double faults in the second brought Stephens back into contention as Azarenka lost three consecutive service games.
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Stephens made short work of her opponent in the deciding set taking it 6-1.
Jelena Ostapenko will be her opponent after she beat qualifier Danielle Collins 7-6, 6-3.
Collins had already seen off Venus Williams in the quarter-finals but met her match against the Latvian, who was ruthless in the first set tie-break breaking her four times as Ostapenko took the first set.
The second was less of a dogfight - the world number five breaking Collins in the opening game and closing out the set on the first match point.