The Oamaru junior driver has driven a personal-best 65 winners this term and he is the leading junior driver in the absence of Dexter Dunn (220).
He is seventh in the overall list of drivers.
Williamson (21) was runner-up in the Australasian Young Drivers Championship held at Forbury Park, Addington and Ashburton last month.
Last week he won the Darren De Filippi Memorial Pace, an established race for junior drivers at Addington.
Williamson is close to completing his third season as a reinsman. He had 27 wins in his first season and 46 last season.
Williamson has drawn Pammy's Boy, El Zhar and Westburn Splendour in the three heats of the championship tonight.
Westburn Splendour was a last-start winner at Addington on July 5 when driven by her trainer Jamie Keast. She has been scratched from race 10 tonight.
Pammy's Boy, who has not raced since March 6, won a trial at Rangiora last week.
El Zhar has been away from racing since January. He won first up at Addington in December for West Melton trainer and part-owner David Pearce.
Joshua Dickie, winner of the Australasian Championship and Zac Butcher, winner of the New Zealand Championship two years ago, are competing against Williamson tonight.
Williamson has been engaged to drive Carter's Rocket and Double Happy by trainer Cran Dalgety, whose right-hand man Dexter Dunn is in the United States.
Williamson drove Double Happy to finish fourth last week.
"I like the way Matty is progressing. He is an up-and-coming talent," Dalgety said.
Dalgety is concerned about a second-line draw for Carter's Rocket, who is having his first start. The rising 3yr-old has won a trial and a workout in the past fortnight.
• JB Maguire has been scratched from his engagements at Addington and Rangiora after being sold out of the Dalgety stable to clients of Sydney trainer Peter Morris.
JB Maguire has won five races and been six times placed in 14 starts since he began racing in October. The 3yr-old son of Bettor's Delight and Mystic Gold was raced by Cambridge breeders Ray and Diana Kennedy with Chrissy Dalgety.
Morris won 40 races, including a South Australian Cup with the New Zealand-bred Young Mister Charles (Paulsboro-Miss Manette) in the 1990s.
Lightning Raider, who won 10 races when trained by Dalgety, has made an immediate impression after being sold to Australia late in May. Trained by Luke McCarthy, the Christian Cullen-Talent Hanover 5yr-old won the $A45,000 Four and Five-Year-Old Championship at Albion Park last Saturday after wins at his two other starts in 1.54.3 at Menangle.
