Vera Zvonareva sent world number one Maria Sharapova to a stunning 4-6, 7-5, 6-1 defeat in the fourth round of the Pacific Life Open on Tuesday.

In one the greatest collapses of her career, the defending champion failed to close out the match when 5-3 ahead in the second set and then completely lost control, giving up eight games in a row.

Sharapova ended the all-Russian contest with 47 unforced errors, including 13 double faults.

With the defeat, the 19-year-old is guaranteed to lose her number one ranking to Belgium's Justine Henin next week.