Williamson is heading to San Francisco to start a contract with women's pro team Vanderkitten.
She had a slow start to the year due to injury but rode well on Saturday to win the women's race in the third round of the Benchmark Homes-sponsored elite series in Canterbury.
Williamson (H & J Smiths) held off the series leader, Olympian Lauren Ellis, in a tight uphill finishing sprint in the 99km race between Culverden and Kaikoura. Her winning time was 2hr 41min 32sec.
''It wasn't the ideal start to the year, but the form seems to be coming along all right and I'm really excited to be heading away on Wednesday,'' Williamson said.
Williamson, who said she was feeling good on the climbs all day, was part of a breakaway group of six riders that contested the final climb to the finish line that included Ellis, round one winner Sharlotte Lucas, Kerri-Anne Torkler, Hayley Mercer and Laura Fairweather.
Otago cyclist Joe Chapman maintained his lead in the series with a third placing in the 133km men's race that started at Hanmer Springs.
Tom Hubbard, who had finished second in the previous round in Nelson, won the race in 2hr 51min 29sec. James Early was second, 5sec off the front, with Chapman a further 1sec back.
Glen Rewi won the masters race, and moves up to second overall behind series leader Lee Johnstone. Otago's Mark Spessot is fourth overall, but has given the over-45 masters yellow jersey to Blair Stuthridge.
The series resumes in Hokitika on August 10.
