Miami: Former world number one Venus Williams, idled for six months, upset Czech third seed Petra Kvitova 6-4, 4-6, 6-0 on Friday to reach the third round of the USD 9.6 million WTA and ATP Miami hardcourt event.

Seven-time Grand Slam champion Williams, in her first WTA event since pulling out of last year's US Open, took advantage on 9-of-11 break-point chances and fought off a rally to advance after two hours and 18 minutes.

Williams booked a third-round matchup with Canadian wildcard Aleksandra Wozniak, who defeated Romania's Monica Niculescu 4-6, 6-3, 6-4.

At last year's US Open, Williams withdrew after a first-round triumph and revealed she had been diagnosed with the auto-immune disorder Sjogren syndrome, an illness that saps her energy and causes pain in her joints.

She played doubles for the US Fed Cup team last month and defeated Japan's Kimiko Date-Krumm 6-0, 6-3 in her WTA return match on Wednesday in round one.

In a later match, Spanish second seed Rafael Nadal will begin his quest for a first-ever Miami title against Colombia's Santiago Giraldo. The winner books a third-round encounter with Czech Radek Stepanek, who ousted Germany's Tommy Haas 7-6 (7/4), 6-1.

World No. 1 Victoria Azarenka of Belarus beat Dutchwoman Michaella Krajicek 6-3, 7-5. Azarenka broke as Krajicek served for the second set, then held and then broke again at love to close out the match after one hour and 42 minutes.

Azarenka stretched her season-long win streak to 24 matches. She has the best start to a WTA season since Martina Hingis won 37 in a row in 1997.

Top seed Azarenka will next face British wildcard Heather Watson, who defeated Czech 27th seed Lucie Safarova 6-2, 6-1.

Azarenka comes off her fourth title of the season at Indian Wells, where she beat World No. 2 Maria Sharapova of Russia in the final just as she did last year in Miami.

World number four Andy Murray eased into the third round by dispatching Colombia's Alejandro Falla 6-2, 6-3, avoiding a repeat of an embarassing first-match ouster in Indian Wells by Spaniard Guillermo Garcia Lopez.

Murray, 24, will next face big-serving Canadian 26th seed Milos Raonic, who advanced over France's Arnaud Clement 7-6 (9/7), 6-2.

The Scotsman won his 22nd ATP title at Brisbane in January and fell to Roger Federer in the Dubai final earlier this month.

Fourth seed Murray, the 2009 champion in Miami when he defeated Serbia's Novak Djokovic, recorded his 15th match win of the season against three defeats, hitting four aces for victory in 77 minutes against Falla.

World No. 1 Djokovic, winner of the past three Grand Slam men's singles titles, will open defense of his Miami crown on Saturday against Marcos Baghdatis of Cyprus.

Russia's Alisa Kleybanova, a former top-20 player who missed the past 10 months battling Hodgkin's lymphoma, was ousted in her second-round match by compatriot Maria Kirilenko 7-6 (7/1), 6-3.