Impervious won on her debut over fences and then took a Grade Two contest against her own sex last time for Murphy, leaving her to carry a penalty amongst a field of geldings.
That burden was largely negated by her mares' allowance, and under Brian Hayes the seven-year-old started at 3-1 for the Grade Three contest.
Locked in a run for the line with Henry de Bromhead's Journey With Me, Impervious battled to get her head in front and eventually prevailed by half a length with the rest of the field 22 lengths or more behind.
As a result, Impervious is now the sponsor's 6-4 favourite for the Mrs Paddy Power Mares' Chase at the Cheltenham Festival.
"I'm delighted with that," said Murphy.
"It was a tall order giving weight to those boys.
"It was probably a little, tiny worry running her on heavy ground too, but she's answered a lot of questions. We can make more plans now.
"She's one of those, she wears her heart on her sleeve and she gives everything."
When asked if she would go straight to the Cheltenham Festival the trainer added: "Without talking to the lads I'm guessing so. I'll have a word with Frank (Berry, racing manager) and JP (McManus, owner) and see then.
"She seems to be improving and especially with those fillies, when they start improving you don't know where they'll end up but I do know it's nice to have her."
Royal Thief returned from a 782-day absence to land the Total Event Rental Amateur National for Patrick Mullins and Henry de Bromhead.
The gelding made a winning start to his chasing career in 2020 before being brought down on his next run and he had been off the track since.
Mullins' mount was a 14-1 chance and took no time to hit his stride after the long lay-off, jumping well and prevailing by 10 lengths.
"I'm delighted with that. Patrick was brilliant on him," said De Bromhead.
"He said there was a fresh strip out at the wing and he went that way so fair play to him. It worked really well.
"He hadn't run for a long time so it's great and I'm delighted for (owners) Gigginstown. He ran well in the Pertemps a few years ago, then won his beginners' chase and got hurt.
"We're in no panic with him now, we'll enjoy today and have no major plans."