Billy won the TheraPlate UK Liverpool International Grand Prix for a remarkable third time in five years after an exhibition of world-class showjumpjng at the M&S Bank Arena.
Billy, one of the most consistent Irish riders of his generation, followed Liverpool grand prix wins with Diaghilev in 2015 and 2016 by scooping a £26,000 top prize.
He triumphed in the jump-off on Kimba Flamenco by almost two seconds from 18-year-old British prospect Jack Whitaker, riding Elucar V.E. and British Tokyo 2020 Olympic hopeful Holly Smith, who was third aboard Hearts Destiny.
Course designer Alan Wade's brilliant track tested every combination in a 31-strong field, with just six making it through to the jump-off.
And Billy showcased all his experience to preserve an amazing record of every Liverpool grand prix either being won by himself or fellow Irishman Shane Breen.
"To win the grand prix three times here is amazing," Billy said.
"My horse jumped fantastic. He has been close to doing something in the last couple of shows, and finally it has paid off for me and him here.
"I am delighted for the owner and everyone involved with the horse. A win always helps everything.
"He is an extremely talented horse. He has won a CSIO five-star grand prix in Falsterbo, so he is winning at every level, which is good.
"The course builder is probably the best course builder on the planet. He made it difficult enough that it wasn't a giveaway to anyone. You needed to jump the course. It wasn't a rat-race.
"In the jump-off, I tried to put it up to the rest of the riders. Sometimes, when you go early, you don't really know, but thankfully I held on to clinch the win."