Walsh became available after his intended mount, the Willie Mullins-trained Rubi Ball, was a surprising absentee from the five-day declarations for the Grade One feature, returning lame from a schooling session at Punchestown.
With Boston Bob, owned like Tidal Bay by Graham Wylie, also taken out Mullins was left without a runner and Walsh was suddenly hot property.
It was his former boss Nicholls, who until this season had shared Walsh’s services with Mullins, who was first to snap him up for the veteran Tidal Bay.
The 13-year-old ran a blinder in the Welsh Grand National to show he has lost none of his ability and on his only previous visit to Leopardstown he won the Lexus Chase.
“It’s a small field, good prize money, he’s one from one at the track and he’ll get his ground,” said Nicholls.
“Of course Ruby being available also helps, so it has worked out for us.
“Mr Wylie will have some other runners on the card as well so it made sense to run really.”
Rubi Ball’s defection leaves a field of seven possible runners, with Lexus runner-up First Lieutenant the likely favourite for Mouse Morris.
Morris said: “He is all set to run on Sunday. He is in great form and this race has been the plan since he ran at Christmas time.”
First Lieutenant’s owners, Gigginstown House Stud, have a formidable hand with Philip Fenton’s Last Instalment and the Gordon Elliott-trained Roi Du Mee also in contention.
Jim Culloty’s Lord Windermere, Dessie Hughes’ Lyreen Legend and the Noel Meade-trained Texas Jack complete the confirmations.
Carlingford Lough, Champagne Fever and Don Cossack are among seven possible runners in the Dr PJ Moriarty Novice Chase at Leopardstown on Sunday.
The John Kiely-trained Carlingford Lough was last seen winning the Topaz Novice Chase at Leopardstown’s Christmas meeting, while Don Cossack’s most recent appearance was his victory over Carlingford Lough in the Drinmore Novice Chase at Fairyhouse at the start of December.
Don Cossack’s trainer Gordon Elliot said: “He’ll go for the Moriarty on Sunday. He seems well, touch wood.”
Champion trainer Willie Mullins still has Ballycasey and Champagne Fever in the mix, while Dessie Hughes’ Bright New Dawn, the Ted Walsh-trained Foxrock and Henry de Bromhead’s Sizing Gold complete the acceptors.
The unbeaten Faugheen is one of five potential runners for Willie Mullins in the Deloitte Novice Hurdle at Leopardstown on Sunday.
The champion trainer saddled Champagne Fever to take the Grade One prize 12 months ago before his success in the Supreme Novices’ Hurdle at Cheltenham and appears intent on taking the prize once again.
Faugheen has barely come off the bridle in three starts over obstacles and appears bound for the Neptune Investment Management Novices’ Hurdle at Cheltenham in March.
Mullins also has Vautour, who carries the same colours of Susannah and Rich Ricci, together with Arctic Fire, Renneti and Valseur Lido.
The Tullow Tank, already a dual Grade One winner this term for Philip Fenton, looks the biggest threat to the Mullins brigade.
Fenton reports The Tullow Tank to be super form as he bids for his third Grade 1 success of the season.
Fenton said: “He has surprised us this season. Last year he looked average and he was still developing but fair dues to Barry [Connell], we took our time with him and those couple of runs over hurdles last season have helped him to grow up.
“When he won his bumper last season we felt that he might develop into a novice hurdler this season, but we didn’t expect him to be a Grade 1 horse. He has had a clear run since Christmas.”
The 11 entries are completed by Eoin Griffin’s Azorian, Tony Martin’s supplemented Quickpick Vic, Dessie Hughes’ Art Of Payroll, John Ryan’s Draycott Place and Pat Shanahan’s King Of The Picts.
Triumph Hurdle favourite Ivan Grozny is one of eight possible runners in the Gala Retail Spring Juvenile Hurdle at Leopardstown on Sunday.
Willie Mullins French Flat recruit was narrowly beaten by the Aidan O’Brien-trained Plinth on his jumping debut at Leopardstown’s Christmas Festival, but showed he had benefited from the outing with a brilliant display at Naas last month.
Plinth, not seen since his festive triumph, is set to reoppose in the Grade One contest.