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.
Spanish second seed Rafael Nadal began his quest for a first-ever Miami hardcourt title by ousting Colombia's Santiago Giraldo 6-2 6-0 in 69 minutes.
Nadal, who received a first-round bye, advanced to a third-round match with Czech Radek Stepanek, who ousted Germany's Tommy Haas 7-6 (7-4) 6-1.
World No.4 Andy Murray eased into the third round by dispatching Colombia's Alejandro Falla 6-2 6-3, avoiding a repeat of an embarrassing 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.
Fourth seed Murray, the 2009 champion in Miami when he defeated 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 will open defence 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.
-AAP