Alfie Sherrin won the JLT Specialty Chase at the Cheltenham Festival.
Fruity O'Rooney had led from flagfall and put in a gallant front-running display, jumping the last in the lead before being mugged on the run-in by Alfie Sherrin.
The winner was going away at the line and won by a length in the end, with Fruity O'Rooney four lengths clear of Our Mick in third.
The Package was well-backed and ran well in fourth.
McLernon said: "The work the teams at Jackdaws (O'Neill's yard) and Martinstown (owner JP McManus' stud) put in is absolutely brilliant.
"He jumped absolutely super. I was told to ride him with loads of confidence and get round if you can.
"That's what I did and they are brilliant people to ride for."
O'Neill said: "It's great and lovely to get a winner at Cheltenham. We're relieved as yesterday morning we didn't think he would get in, but he did.
"It's great for Richie. He gave him a brilliant ride."
McManus said: "Jonjo bought him at the horses in training sale at Doncaster as he thought he was worth taking a chance on.
"He's had his issues, but he got it right here today.
"Full marks to Jonjo and all of the lads at Jackdaws Castle, they've put the work into him and it's turned out well.
"Jonjo said he was in good form and don't be surprised if he runs a big race.
"He said he's just getting his act together."
It was a first Festival winner for McLernon, who continued: "The ground was coming right and the horse was just coming to himself at home.
"The team are in absolutely great shape. Jonjo said go out and be confident.
"The team have done so well to get him here as he is a horse with a few niggly problems.
"Mr O'Neill is the man for the day.
"You come in here and you see people you haven't seen for years and they're absolutely delighted for you. It's brilliant.
"We get up at 5.30am every morning and everyone in the yard works very hard. It's brilliant that you can come here and produce it on the day.
"AP McCoy helps me out so much and he was one of the first people up to congratulate me."
O'Neill added: "We really wanted to run him in the Pertemps but he wasn't going to get in that.
"Any winner at Cheltenham is brilliant and this is a good horse, who's had problems with his hocks, with his stifle, his joints, everything.
"He could be a National horse one day, you never know."
McManus, who was also represented by Quantitativeeasing, said: "I backed neither of them. I wanted to back this horse at 25-1 this morning, but when I rang my bookmaker the price had dropped. so I said I'd just cheer him on."
Gary Moore was disappointed to see Fruity O'Rooney lose out in the shadow of the post.
He said: "I'm absolutely gutted for all of us, myself, Jamie (Moore) and the owners.
"He's done everything right and the last horse to challenge him has beaten him. Maybe if he wasn't pressed for the lead throughout, he would have held on.
"He's so much better left-handed so we might go to Aintree.
"We were beaten by a better-handicapped horse on the day."
In contrast, Donald McCain was delighted with the effort of third-placed Our Mick.
He said: "He missed the two fences at the top of the hill and you would have to say that has cost him.
"He got the trip well and he's run a screamer.
"I didn't think he was well handicapped either so he's run a huge race."
A tilt at next month's John Smith's Grand National is now on the cards for The Package.
David Pipe said: "He's run a cracker. At one stage I thought he was going to do it. I expect we will go the National next."