Novak Djokovic stretched his winning streak to 24 straight matches with an emphatic victory over Kevin Anderson to reach the Miami semi-finals on Wednesday.

The win also avenged a loss two years ago to the South African in the same city.

Djokovic, the world number two, defeated the unseeded Anderson 6-4 6-2 in a quarter-final match at the $US9 million ($A8.74 million) ATP Masters 1000 hardcourt tournament.

"When I was two breaks up in the second set I was comfortable sure, but not before that," Djokovic said.

"In the second set I found that momentum, but I went through situations where I faced a couple of break points in the first and second set, and I saved them.

"I was fortunate in those moments."

Djokovic, who has won all of his 22 matches this season, will face American Mardy Fish in the semi-finals.

Djokovic's winning sequence dates back to last year's Davis Cup final.

"You obviously get confidence with 24 wins in a row," he said. "It keeps getting better. But I don't want to be carried away with that.

"I want to keep on working hard and taking one match at a time. When it stops, it stops."

The Serb is looking for back-to-back titles in Indian Wells and Miami. It would be his fourth title this season to go with victories in Dubai, Indian Wells and the Australian Open.

Djokovic will be the heavy favourite against 14th seeded Fish who will pass Andy Roddick as the No.1 ranked American player when the next ATP Tour rankings come out.

Fish has had an up and down year, making two semis in Delray Beach and Memphis, but losing in the second round of both the Australian Open and Indian Wells.

He lost twice this year to 20-year-old Milos Raonic of Canada in the second round at Indian Wells and the semis in Memphis.

Fish ousted an ailing David Ferrer 7-5 6-2 to reach the semi-finals.

The victory ensures Fish will climb to at least 11th when the rankings are next released, while Roddick will fall from eighth to 14th after losing his tournament-opener last week.

In women's play, eighth-seed Victoria Azarenka toppled defending champion and second seed Kim Clijsters to reach the semi-finals.

Azarenka, of Belarus, defeated the ailing Clijsters 6-3 6-3 to reach her first semi-final of the season.

In the semi-finals she will face third-seeded Russian Vera Zvonareva, a 7-5 6-3 winner over Poland's Agienszka Radwanska.

Belgium's Clijsters had eight double faults and held her serve just three times in nine service games on Wednesday as she continues to be bothered by a right shoulder injury. The shoulder has troubled her since January when she won the Australian Open.

Azarenka's biggest career win came in 2009 when she captured the Key Biscayne title.

The other semi-final features Russia's Maria Sharapova squaring off against rising German star Andrea Petkovic.

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