Updated

Singapore (SportsNetwork.com) - Serena Williams avenged an earlier loss and captured the season-ending WTA Finals trophy with a scorching defeat of Simona Halep on Sunday.

The two had met earlier this week in round-robin play, and the 6-0, 6-2 Halep rout in 65 minutes equaled the worst loss of Williams' career.

Williams, though, returned the favor on Sunday as she blitzed the Romanian 6-3, 6-0 in just 69 minutes for her 64th career title and fifth title at this event.

The 33-year-old American has won the past three WTA Finals titles, and also claimed the crown here in 2009 and 2001. She finished as a runner-up in 2002 and 2004.

Williams had already clinched the year-end No. 1 ranking on Friday and improved to 4-1 against Halep in her career.

At first it appeared that Halep was up to the task in the rematch, taking the first two games in the first set.

Williams, though, rallied to win six of the next seven, then breezed in the second set to ensure there would be no repeat of the round-robin defeat.

"She was playing so well at the beginning and I told myself to just relax and once I did that I started playing better and making my shots," said Williams.

Halep fell to 8-6 all-time in finals, including 2-3 this year.