The popular 11-year-old ended a losing streak going back almost three years when storming up the hill at the Esher course to beat the previous year's winner Pete The Feat in the 32Red Veterans' Handicap Chase Final.
The victory resulted in the assessor raising him to a mark of 145 from 138.
"It was a tremendous run. I'm over the moon with him," said trainer Evan Williams.
"He's in fantastic form and will go for the Grand National now. We'll have a pop at it."
Buywise completed the course when 12th of 16 finishers behind Rule The World in his previous try at the Aintree spectacular in April 2016.
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