Having only her third race over jumps, the five-year-old toyed with the opposition as she completed a treble on the day for the Mullins team and owner Rich Ricci.
Walsh coaxed her to the front at the last and sealed the newest race of the Festival in a matter of strides.
Limini (8-11 favourite) powered up the hill to strike by four and a half lengths from Dusky Legend (50-1) with Bloody Mary (7-1) third, as Mullins and Walsh secured their seventh success of the week.
Mullins said: “We couldn’t believe we could buy her with just one bid at the sales, a mare with her potential.
“She was very novicey on her first run but every time she worked she showed how good she was and her jumping improved each time we schooled her and for a novice having just her third run she was very good today.
“It looked like she liked the better ground.
“She’s got a nice Flat mark and the Ascot Stakes would look a target, however, we will look at Liverpool, Punchestown or maybe both depending how she is.
“She’s plenty of stamina and lots of speed.”
Meanwhile, Empire Of Dirt powered through the field to give Bryan Cooper his first winner of the meeting in the Brown Advisory & Merriebelle Stable Plate Handicap Chase at Cheltenham.
Cooper brought Colm Murphy’s nine-year-old with a steady run on the outside to put in a challenge from two out. Empire Of Dirt (16-1), wearing the Gigginstown House Stud colours, kept on stoutly up the hill to beat Tango De Juilley by four lengths.
Kings Palace put up a solid performance to take third place a length and a quarter away, while Full Shift was fourth.
There were several casualties, including Stilletto unseating his rider at the third, Darna falling at the eighth fence, bringing down Bear’s Affair and badly hampering Fingal Bay, while Niceonefrankie came down at the fourth-last.
Cooper expressed delight at having secured his first Festival winner of the week.
He said: “It’s just a relief. I’ve had so many good rides, to be fair. I know the horses are running as good as they are - they are just coming up one or two better ones.”
Of Empire Of Dirt, Cooper said: “They went a good gallop and he won with a fair bit up his sleeve.”
Murphy said: “I was a bit animated coming down to the last, it’s fantastic.
“He’s hit the ground a few times along the way but he’s been a good buy”
Empire of Dirt was bred by Sean Harnedy, father of Cork hurling star Seamus.
Cause Of Causes gave the Irish their sixth winner on St Patrick’s Day when storming home in the Fulke Walwyn Kim Muir Challenge Cup Handicap Chase.
Victorious in the four-mile National Hunt Chase 12 months ago, Cause Of Cause (9-2) came from way off the pace to turn this three-and-a-quarter-mile test into a procession.
He still had plenty to do at the second-last but made up a massive amount of ground to lead before the final fence.
With his stamina not in question, Cause Of Causes pulled clear on the flat to win by 12 lengths from A Good Skin (14-1) for trainer Gordon Elliott and owner JP McManus. Silvergrove (16-1) was half a length back in and Knock House (16-1) was fourth.
It was Jamie Codd’s fourth victory in race after Character Building in 2009, Junior in 2011 and The Package 12 months ago.
Widely regarded as the best amateur in the business, lesser jockeys may have panicked with a mile to run but Codd knew his mount stayed strongly having won over four miles on him last year.
The favourite, Doctor Harper, made several errors before falling late on.
Codd said: “He’s been a great horse for me, he won here last year.
“Gordon had him in unbelievable form, I’ve been riding him a couple of times a week, he loves this time of year, he thrives.
“I’m very grateful to JP (McManus), Gordon’s team are fantastic and it’s an honour to work with them.”
Elliott, who lost star novice No More Heroes to injury after his run in the RSA Chase, said: “It’s been up and down, but we have to keep our head up.
“We’ve been in the enclosure with five or six.
“I’ve had him since he was four and he’s run in all the big races, I’m lucky to have him.”