Miami, Mar 27 (IANS/RIA Novosti): Germany's Tommy Haas stunned top-ranked Novak Djokovic with a straight-sets victory that propelled the 15th-seeded veteran to the quarterfinals of the Miami Masters.

With the 6-2, 6-4 win Tuesday, Haas, 34, became the oldest player to beat a World No.1 in more than three decades.

"I'm just really happy and proud of that tonight, against such a great player who has been dominating the sport the past couple of years. I really took advantage of the opportunities I've gotten. I think I played extremely well. He gave me a lot of looks, and I took advantage of it," Haas told the ATP website.

In Wednesday's quarterfinals, Haas faces France's Gilles Simon, who beat Janko Tipsarevic 5-7, 6-2, 6-2.

Elsewhere, last year's runner-up Andy Murray defeated 16th-seeded Italian Andreas Seppi 6-2, 6-4 to book a quarterfinal encounter with ninth-seeded Marin Cilic. The 24-year-old Croatian scraped past sixth-seeded Jo-Wilfried Tsonga 7-5, 7-6(4).

David Ferrer, the third seed, disposed of Key Nisikori 6-4, 6-2 and will play the tournament's remaining non-seeded player Jurgen Melzer, who beat Albert Ramos in straight sets.

In the women's draw, World No.1 Serena Williams beat Australian Open runner-up Li Na to reach the semifinal. Despite 31 unforced errors, Williams finished off her opponent in two sets 6-3, 7-6(5) and faces reigning champion Agnieszka Radwanska in the semis.

Radwanska, the fourth seed, had rallied from one set down in her quarterfinal clash with Belgium's Kirsten Flipkens for a 4-6, 6-4, 6-2 victory.

The Miami Masters, known as the Sony Open for sponsorship reasons, is a hard-court WTA Premier Mandatory tournament with a $5.2 million prize fund. For the men, it is an ATP 1000 event offering $4.3 million in prize money.