The nine-year-old was sent off a 10-1 chance for the extended four-mile feature and was settled in behind in the opening exchanges as Shotgun Paddy and Straidnahanna went toe to toe for the early lead.
A bad early error saw Shotgun Paddy drop slightly off the pace, with jockey Daryl Jacob doing well to maintain the partnership, and it was Stradinahanna who set a decent gallop on what was testing ground.
However, his early exertions began to take their toll and with the field suitably thinned out and four obstacles left to jump, Robbie Dunne seized the initiative on Mysteree.
While Knockanrawley, who had also been prominent, and Shotgun Paddy tried to go with him, Mysteree took a couple of lengths out of them on the turn for home and kept up his gallop admirably.
Mysteree slightly began to falter after the last, but Knockanrawley could not get back on terms, going down by four lengths.
Shotgun Paddy, the 6-1 favourite, claimed third with Harry The Viking plugging away for fourth.
Scudamore - who celebrated his 33rd birthday on Friday with victory in the Devon National courtesy of Kingswell Theatre - could now look towards the Coral Scottish National on April 22 at Ayr, but admits ground conditions may not be suitable in the spring.
He said: "He slogged it out and did it the hard way in pretty tough conditions.
"He was fourth in this race last year, but is another year older and stronger this time. It was a nice performance when he won at Haydock (on his penultimate start), he's come on from that and Robbie has given him a great ride.
"There are no concrete plans now. All being well, we will probably give him an entry in the Scottish National but that will obviously depend on the ground. The last few years it has been good, good to soft ground so hopefully we could be due a softer one this year.
"If that doesn't work out, he's won two nice prizes this year and he can just be put away with things like the Welsh National in mind next season."
