The top-seeded Williams beat fellow American and second seed Lindsay Davenport for the third time in the final at the Connecticut Tennis Center at Yale, 7-5, 6-0, and collected the top prize of $93,000 in the $585,000 event.
The 22-year-old Williams became the first player to win the same WTA event four straight times since Monica Seles took the Canadian Open title from 1995-98. She also became just the ninth woman in the Open Era (since 1968) to capture the same title four consecutive years.
The second seed at the U.S. Open, which starts Monday, Williams likely will have confidence that she can lift the trophy for the third straight year at Flushing, N.Y. She will enter the final Grand Slam event of the year with a 13-match winning streak.
The four-time Grand Slam titlist captured the Stanford and San Diego hardcourt crowns in her previous two outings.
Williams extended her winning streak over Davenport to five matches and edged ahead in their all-time series, 11-10.
Davenport, who was sidelined for nearly nine months while recovering from knee surgery, was competing in her fourth WTA event of the season. Since her return, Davenport also has reached the final at Los Angeles and the last four at Stanford and San Diego.
The 26-year-old Davenport, who also lost to Williams here in the 1999 and 2001 finals, was unable to win the tournament for the second time. She won in 1997, the only year the event was held in Atlanta and the last time it took place outside New Haven.