The pacer made it four wins from just six career starts when heading a quinella for veteran Canterbury trainer Warren Stapleton. Lester ran into second.
After enjoying a sweet run in midfield for much of the event, Wild Willow needed to be extricated from a tricky spot at the 600m, which May was able to do with ease.
"I got a reasonably good run.
‘‘I got out down the back and he sprinted the best," the reinsman said.
"I thought the stablemate was jogging beside me coming around the bend and I thought he would be the hardest to beat but he never got past me."
Owners Phil and Margaret Creighton, Ken Cummings, Greg Hope and John and Jenny Grainger have had to be patient with their talented pacer.
Wild Willow began his career at Mark Purdon’s All Stars Stable before moving to Greg and Nina Hope’s barn and then on to the Stapleton stable.
Stapleton is renowned for his ability to patch up an injury-plagued horses and he has again worked his magic on Wild Willow.
Tendon and ligament injuries had limited him to three starts in just under two years leading into the Oamaru Cup.
"For a horse that has only had six starts, to win four of them is a big effort alone," May said.
"[Warren] has certainly done a marvellous job on their legs."
Arafura produced one of the more spectacular wins on Oamaru Cup Day when claiming the Denice Swain Memorial.
The 2-year-old loomed up on the home turn and then ducked in and broke, seemingly ruining her winning chances.
But after getting rebalanced by driver Bob Butt, Arafura charged late to record a stunning win in just her second career start.
The victory continued a successful weekend for both trainer Hayden Cullen and driver Bob Butt.
Butt combined with Bet N Win, who justified his favouritism for the group 3 Canterbury Park Trotting Cup with an easy victory which guaranteed his place in next month’s group 1 Dominion at the same track.
Yesterday’s edition was the inaugural running of the Denise Swain Memorial following her death in Invercargill late last month.
A multiple group-race-winning trainer, Swain was the first woman to start a horse in the New Zealand Cup, Clancy going on to run second.