Williams beat Italy’s Flavia Pennetta 7-6 (1), 6-2 to take the tournament she last won as a teenager in 1999.
The win should seal the 28-year-old American’s place at the season-ending WTA Tour Championship in Doha next month. She also won at Wimbledon this year.
“I love the pressure,” Williams said. “I need it in my life.
“It is great to come here and play my best tennis of the week in the final against someone who is playing as well as she is.”
Pennetta had upset top-ranked Jelena Jankovic in the second round and went in with a 3-1 career record against Williams after beating her in Moscow last week.
“She just played unbelievable today,” the 17th-ranked Pennetta said. “It is tough to play against someone who serves like she did today. I didn’t have any chance to make any breaks.”
The first set stayed on serve, with neither player allowing a break point opportunity.
Williams dominated the tiebreaker, racing to a 6-0 lead. Pennetta saved one set point but then netted a backhand.
Williams created her first break chance at 1-1 in the second set, and Pennetta netted another double-fisted backhand.
In the next game, Williams delivered four straight aces.
“I have never had one of those games before,” she said. “That was obviously a great moment.”
Serving at 5-2, Williams let her first match point slip away when she allowed a backhand from Pennetta to pass her, thinking it would land long.
A forehand winner created a second chance, and her next serve was too powerful for Pennetta to handle.
Williams said she would return to Florida before the Nov. 4-9 Tour finale in Qatar.
“I will go home and rest a little bit and continue to prepare and get ready for Doha,” she said.
Williams is expected to climb one place to No. 8 when the new WTA rankings are published Monday; Pennetta hopes to rise three spots to a career-best 14th.
The 26-year-old Italian was trying to become the third player to beat Williams for a fourth straight match. Only Serena Williams and Lindsay Davenport have achieved the feat.
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