Mr Mor's dogged finish saw him down Brer by four lengths with third place going to Get Flash, whose stablemate and favourite I've Got This was never in contention and was pulled out of the contest.
While Mitchell may have had his concerns with Mr Mor, co-trainer JJ Rayner was more relaxed.
"That's just how he is - he's hard work and then he gets his second wind and he gets going again," she said. "He's our favourite."
Rayner, who prepares Mr Mor at Wanganui with her father Evan, said they had expected a bold showing from the gelding, who had improved with his previous outing for fourth in the Manawatu Steeplechase.
"He needed that run and we'll go to Trentham now."
Mr Mor will step out in the Wellington Steeplechase in a fortnight's time before heading south for the Grand National Steeplechase on August 13.
Twelve months ago, he won the Trentham event before finishing runner-up to High Forty at Riccarton.
- NZ Racing Desk