The son of Jeremy looked a serious Classic contender after winning both the Ballysax Stakes and the Derrinstown Stud Derby Trial a couple of years ago, but suffered a serious injury in the Epsom Derby won by Golden Horn.
A listless effort in Germany on his comeback run later that year suggested his career may be jeopardy, but he has been a model of consistency in the last two seasons, beating Champion Stakes winner Fascinating Rock and chasing home Arc heroine Found along the way.
Victories have proved difficult to come by, but with the rain-softened ground in his favour, the five-year-old grey was the 3-1 favourite for York's Group Two feature.
Shane Foley set the fractions in front and while the globetrotting Mondialiste finished with a real flourish, Success Days refused to bend and clung on by a nose.
Condon said: "To be honest I thought we were booked for second half a furlong down, but he's really dug deep.
"He's such a tough and consistent horse. He'd been narrowly beaten in two Group Threes this year, but today was his day. He's at the ceiling of his ability now.
"Not many horses come back from what happened to him at Epsom. He fractured his pastern and had to have six weeks box rest.
"He's lightly enough raced, but soft ground is important to him."
Success Days holds an entry in the Juddmonte International back at York on August 23, but looks unlikely to make a return trip.
"He's a solid 114-rated horse and I'm not sure he'd be good enough to win a race like that, plus the ground will probably be quick here by then," Condon added.
"Champions Weekend at home is important to us. He's in the Irish Champion Stakes (Leopardstown, September 9) and there's also a mile-and-a-half Group Three and the Boomerang Stakes over a mile.
"I wouldn't mind having a go at the Champion Stakes at Ascot if it came up soft, but we might have to travel abroad with him if he is going to win a Group One.
"He went to Germany before and it didn't work out, but the race in Munich in November (Grosser Preis von Bayern) would probably suit him."
There was a sting in the tail for tail for Foley, with the stewards handing him a six-day ban for using his whip above the permitted level and in the incorrect place.
Flying Pursuit (12-1) led his rivals a merry dance in the £50,000 Sky Bet Dash.
Tim Easterby's four-year-old failed to fire on his latest appearance at Hamilton last week, but ploughed a lone furrow up the Knavesmire and came home a comfortable two lengths clear of Al Qahwa under apprentice Rachel Richardson.
Easterby said: "He's a good little horse, but the ground is the key to him. He loves a bit of cut.
"He was disappointing at Hamilton the other day, he just didn't race at all for whatever reason.
"Rachel gave him a good ride and we'll look towards Ayr (Gold Cup)."
Easterby completed a double with the David Allan-ridden 5-2 favourite Appointed in the Sky Bet Supporting New Beginnings British EBF Fillies' Handicap.
Michael Dods enjoyed an across-the-card treble on Friday, including two winners at York in the evening.
The purple patch continued for the Darlington-based trainer as 4-1 shot Get Knotted landed the Win £100K For Free At sportinglife.com/pick7 Now Handicap for the second year in succession in the hands of Paul Mulrennan.
"He's a good horse on his day and always runs well here," said Dods.
"The plan would be to go for one of the sprints up at Ayr. He was second in the Silver Cup last year and that's where he might end up again.
"That's not until September, though, so we'll try and find him something else beforehand."
The Kevin Ryan-trained Hey Jonesy (11-8), beaten just a nose into second place on his Carlisle debut a fortnight ago, went one better with an emphatic display in the Get The Sky Bet Advantage Novice Median Auction Stakes.
Ryan's son and assistant, Adam, said: "He's so straightforward. He's easy at home and easy on the track and he's turned inside out in the last two weeks.
"I can't speak for the old man, but he's in the sales race over the course and distance (Goffs Premier Yearling Conditions Stakes, August 24) and that would look an obvious target."
Graceful Lady (6-1) claimed her fourth victory of the campaign for trainer Robert Eddery in the Sky Bet Best Odds Guaranteed Handicap, with 17-year-old 7lb claimer Darragh Keenan in the saddle.