Dunn (21) bettered his own record of 204 wins set in the 2008-09 season when he drove JB Maguire, his second win for the day.
It was fitting that JB Maguire is trained by Cran Dalgety, who employs Dunn.
Dunn has driven in 1098 races this season and amassed stakes of $1,722,441.
He has a lead of 75 wins over David Butcher in the premiership.
Dunn drove his first New Zealand winner, Crusader Franco, at Ashburton in November, 2006.
He reached 162 wins for the 2008-9 season at the corresponding Ashburton meeting two years ago, surpassing the record of 161 set by Maurice McKendry in 1988-89.
The horse was Band On The Run, trained by Dalgety.
Dunn had won the Harness Jewels race for 2yr-olds at Ashburton two days earlier on the Dalgety-trained Smiling Shard.
He won the Ashburton Cup on the same horse in December.
Dunn is booked to leave for the United States on July 10.
He hopes to obtain opportunities in New York state as a lead up to the World Driving Championship later next month, when he will represent New Zealand.
"The world championship is on five different tracks and hopefully, I can get some experience of some of them," Dunn said.
Dunn has American contacts including Andy McCarthy, a successful driver.
He is a brother of Luke McCarthy, the driver of Mr Feelgood.
