The 10-1 chance Le Beau Bai put in a strong staying performance to outpace the well-fancied Giles Cross and win the Welsh National at Chepstow.
Trained by Richard Lee and ridden by Charlie Poste, the eight-year-old was third in the race two years ago.
But he and Giles Cross relished the heavy ground and they went clear of the rest of the field a long way from home.
Le Beau Bai went ahead at the second last and stayed clear, with Cappa Bleu and Bench Warrent third and fourth.
Giles Cross, who finished second last year, was keen to go one better this time around under Denis O'Regan and set the pace with Le Beau Bai.
The pair stretched out the field as some of the challengers behind, including recent Hennessy Gold Cup winner Carruthers, struggled to cope with the speed and the conditions.
Although it was Giles Cross who kicked clear on the turn-in for home, Poste kept urging his charge along and after taking the lead he went on to win by seven lengths for the biggest win of Poste's career and only his ninth victory of the season.
"He's been a good servant to me," said Poste afterwards. "Beforehand I spoke to the owners and I picked out Giles Cross as the one I really thought was the one we had to beat.
"We rode him in similar style when he won here earlier this month.
"I never thought it was a foregone conclusion and he's toughed it out really well."