The five-year-old left it late to pip favourite Pont Alexandre in the Neptune Novice Hurdle to give Twiston-Davies his first win at this year's meeting.
However, the 55-year-old has revealed that he only saw the gelding leap the final fence because he was using the toilet.
"I didn't see the race because my guts took hold and I was in the loo," he told BBC Sport. "I only saw the last hurdle. But I'm chuffed to bits. We've done the job right. It's what racing is all about."
The New One was ridden by Twiston-Davies's son Sam.