A frustrated Serena Williams clawed into her 10th Miami final on Thursday, defeating Simona Halep 6-2, 4-6, 7-5.

Williams, apparently rattled by the Halep cheer squad who drowned out most of the chants for the home hope, saw her mighty forehand desert her in the second set, in which Halep converted the only break point of the set to force a third.

World number one Williams, who captured her 19th Grand Slam title at the Australian Open this year, regrouped to seize a 5-2 lead in the third only for the world number three from Romania to battle back.

Finally Williams found a way, and she will bid for an eighth Miami title against Carla Suarez Navarro.

Spain's Suarez Navarro earned her place in the biggest match of her career with a 6-3, 6-3 victory over Germany's Andrea Petkovic.

"I was barely able to regroup," admitted a relieved Williams. "I was making so many errors and was so frustrated.

"The only thing that was working for me was coming to the net. I'm just happy to get through this one.

"Still, it was actually a fun match, I'm in the final so that's unbelievable."

Williams has won all four of her matches against Suarez Navarro without dropping a set.

But she said she'd have to play better to lift the trophy yet again in Miami.

Williams swept the first set with ease before Halep, who captured the biggest title of her career at Indian Wells less than a fortnight ago, found her own rhythm in the second.

In the third, Williams overcame her nerves and flaky forehand to build a 5-2 lead, only for Halep to push the set to 5-all.

However, Williams broke her two games later to pull off the victory.

"I had to dig deep to stay on the court. I could only keep trying," Williams said. "I never gave up and here I am."

Saturday's final will be the biggest career test yet for Suarez Navarro, seeded 12th.

The diminutive Spaniard, who honed her game in the Canary Islands, came out on top in a loose match, combining with Germany's Petkovic for nearly 60 unforced errors in less than 90 minutes on court.

Suarez Navarro, who is now poised to break into the top 10 in the world rankings, converted three of her 10 break point opportunities and was never in serious trouble.

"I played a good match, an important match like this is difficult," said the winner. "I just tried to play my game and enjoy it.

"Playing this final is an important event for me. I train in the off season in hopes of playing a final like this," added the Spaniard, whose only WTA title came in Portugal last year.