Four-times Grand Slam winner Naomi Osaka fired off 18 aces as the Japanese former world number beat Swiss Belinda Bencic 4-6 6-3 6-4 on Thursday to reach her first Miami Open final.

Osaka will next face either American Jessica Pegula or Poland's second seed Iga Swiatek, who meet later on Thursday.

She conceded only two first-serve points in the first set but was unable to convert when it counted as Olympic champion Bencic saved a pair of break points in the second game.

Osaka, who had not dropped a set in the tournament, then lost her serve in the third game and again in the fifth.

The pair traded breaks early in the second set before Osaka seized the momentum after breaking in the sixth game.

"She had a really amazing service return - there were times I thought that I hit great serves but she just hit winners," Osaka said.

"(I was) just battling my inner thoughts and trying to know that I must play one point at a time and, you know, adjust if I have to but try not to overwhelm myself with my thoughts."

Osaka saved five of six break points in the third before closing out the match with an ace and a grin, having reached her first final since her second Australian Open title a year ago.

"I feel like if I was negative for a split second I would have lost the match today," said Osaka, who will play in her fourth WTA 1000 showpiece match on Saturday.

"I have to keep pumping myself up and I haven't played as many matches as a lot of these other players so I just have to keep learning."