Soph was labouring at the 150m under top weight of 58kg after reaching the lead.
McDonald switched his whip from the right to left hand and she responded to win by a length and a-quarter.
"It is something [switching the whip] they do in Europe all the time," McDonald said.
It was among observations McDonald made when riding for three months in Europe this year.
The trip ruled out his the chance of winning the New Zealand jockeys' premiership for a second time, but he ended the season on Saturday in second place with 151 wins, seven behind Opie Bosson.
McDonald led the premiership the previous season with 125 wins.
McDonald (18) has wasted no time in regaining his top billing.
He rode two winners at Ruakaka on his first day back in New Zealand and won the listed Ryder Stakes on Dating at Otaki on Saturday.
He rode two winners at Oamaru yesterday on the first day of the new season.
He is riding on a freelance basis this season after being retained by Te Akau Stables at Matamata under the direction of Mark Walker.
Opie Bosson has taken over as first rider for Te Akau, with Jason Bridgman the trainer and Walker heading to Singapore in January.
"I enjoyed riding for Te Akau and hopefully will still ride some of their horses but I am expecting plenty of opportunities this season," McDonald said.
He has been engaged to ride Taking The Mickey in the $100,000 Winter Cup at Riccarton next Saturday.
Taking The Mickey, a good fourth at Te Rapa on Saturday, won the Winter Cup 12 months ago in the hands of Vinnie Colgan, who is on the sideline with a neck injury.
He fractured his neck in a fall from a horse after the finish of a race at Ellerslie in April.
He had a body brace removed 11 days ago. He is now on a course of physiotherapy. He is a hopeful of a return to riding in September.
McDonald also won on Irish Charmer yesterday.
The Stark South gelding won a 2200m maiden by six lengths after dashing to the front at the 500m.
Soph and Irish Charmer are members of the Wanganui stable of Kevin Myers.
