Chase The Spud came with a late run to lift the staying honours in the Betfred Midlands Grand National at Uttoxeter.
The nine-year-old, trained by Fergal O'Brien and ridden by Paddy Brennan, was the last horse to put in a challenge as Mysteree had led at the third-last in a bid to follow-up his victory in Newcastle's Eider Chase.
The pair jumped the final fence together, but Chase The Spud (11-1) wore down Michael Scudamore's charge on the run-in to get the verdict by a length and a half from Mysteree.
Warrantor was five lengths away in third place, with top-weight Houblon Des Obeaux another two and three-quarter lengths back in fourth.
Brennan said: "For three-quarters of the way, I didn't think I was going to win, but I kept it in my mind there might only be a few finishers and I saved the race for the end.
"I'm so proud of the horse. There has always been an excuse and the owner has been extremely patient. I'm delighted to get a good one for Fergal O'Brien."
Brennan had again suffered disappointment in the Gold Cup at Cheltenham, with Cue Card falling at the same fence as he did 12 months ago.
He added on ITV Racing: "Cheltenham was fine - it just didn't go our way. It's nice to get a big one today."
Speaking afterwards O'Brien said: "We had a good second at Cheltenham in the Pertemps (with Barney Dwan). I was disappointed for Paddy on Friday, but that was yesterday. Today is today and he gave him a fantastic ride.
"That's why I use him. He's been a great friend and I'm absolutely delighted.
"Both horse and rider were tough. Paddy was very strong on him.
"I've got the half-brother and I love the family.
Scudamore was proud of Mysteree, saying: "We managed to beat him a couple of lengths or so at Haydock earlier in the season.
"The weights have turned around and he's come back and done us today, but I'm very proud of our fella. He's come back from the Eider and run a great race and Robbie (Dunne) has given him as lovely ride.
"I'm just proud of the performance."