Albury trainer John Whitelaw produced a brilliant training performance to have The Doctor's Son ($13.00) take out the $40,500 Murrumbidgee Cup (1800m) at Wagga.

The win means The Doctor's Son is exempt from the ballot for the Wagga Gold Cup (2000m) on May 1.

"We were very pleased with his run," Whitelaw said.

"We bred the horse and he's done us proud. Hopefully he runs a good race in the cup. He's doing everything right."

It was a big effort from The Doctor's Son, who had not raced further than 1200m before this preparation.

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His three previous wins, from 12 career starts, had been over 900m and 1000m. It wasn't until he finished down the track at Flemington to kick off this campaign that Whitelaw thought about stretching the five-year-old out.

"It was when I raced him in the city and thought he wasn't quite quick enough," Whitelaw explained.

"He's got a great action and is bred to stay, but you don't know until you try. The funny thing is that when he was winning over 1000 metres it always took them half a lap to pull him up."

Michael Heagney, who had ridden the horse at his four prior starts, stuck strong and got the job done.

The Doctor's Son won by 1.2 lengths from Wyong visitor Brazen ($6.50) and the Mitch Beer-trained River Of Gold ($31), who was a hard luck story from the race.