Bothar Na was gifted victory in the Denny Gold Medal Handicap Chase at Tralee on Thursday.
Waltons Mountain crashed out at the final fence when in command and hampered nearest challenger Monterey Bay.
Bothar Na was left to charge home on the far side under Ruby Walsh to land the 45,000 event.
Mullins revealed that he was straight on the phone afterwards to commiserate with brother Tony, trainer of Waltons Mountain: 'What he said is not for print!'
The winner could head for the Kerry National next: 'The track was a bit sharp for him today. I was thinking about Listowel but I'm a bit worried about the tight track there - although the extra half mile would be a help.'
Mullins was completing a big race double having also claimed the Denny Havasnack (Q.R.) Race with Diego Garcia.
It was a perfect end to the summer for his 16-year-old son Patrick, who was set to head back to boarding school after partnering his 6th winner.
The Sri Pekan gelding completed a four-timer when getting the better of stable-mate Navajo Chieftain inside the final furlong for a length-and-three-quarter victory.
'He could run again at Galway as he handles it so well. My only worry is that it might come too soon. If he doesn't go there he could go to Listowel or the Irish Cesarewitch.'
The other chase on the card also saw the likely winner crash out with Esteban falling two out when looking assured of victory in the Grand Hotel Handicap Chase.
Ichi Beau was left in the lead but couldn't repel the late charge of Mango Catcher, who got up for a length success.
'We were a bit lucky,' admitted winning trainer Paul Nolan. 'But it was also great ride from Paul (Carberry). He dropped out and produced him at the right time.'
Baby Blue Eyes could turn out again at Down Royal on Friday after opening her account in good style in the DNG W.H. Giles Auctioneers Handicap.
Pat Flynn's charge wore down front-runner Dapple Dawn in the final furlong to secure a cosy two-length victory.
'We gave her a break as she was a bit weak. She will be a nicer filly next year,' said Flynn.
Haroni justified the stewards decision to award him the verdict after a controversial finish last time at Tramore when scoring from Golden Future despite shouldering a penalty in the Lee Strand 3-Y-O Hurdle.
Francis Crowley's charge had lost out by a head to that rival on his jumping debut, when hampered close home, but made no mistake this time as he scored by three lengths.
'I knew he would improve from his first run and the track today suited him better than Tramore. I think he's capable of winning another handicap on the Flat but he will probably go for the 3-y-o hurdle at Listowel.'
Luckyvera (9/4f) was a solid favourite in the Timmy Houlihan Memorial Handicap and finished strongly to land the spoils.
Kevin Manning produced the filly inside the final furlong and she got up close home to score by three-parts-of-a-length from Merlins Profit.
Star Inside continued the good form of Kevin Prendergast's juveniles when taking the opening Irish Stallion Farms EBF Median Auction Maiden.
