Smart in his juvenile season - beating Reach For The Moon in the Champagne Stakes - the Roger Varian-trained colt had returned to winning ways in a Listed race at Sandown last time out.
Sent off at 33/1 in the hands of Tom Marquand, he crept into it and showed a smart turn of foot to sweep to a length and a quarter success over Modern Games with Jadoomi a short-head back in third.
John and Thady Gosden's Inspiral started as the 11/10 favourite, but missed the break entirely and never truly looked happy, being beaten a fair way out.
Varian - who was also responsible for fifth-placed at El Drama - said: "It's a funny old game, a funny old game. I need to watch it again, because I was shouting El Drama home, who I thought had a huge chance with two to run. Then I saw Bayside coming and I thought, 'Oh, hang on', and then he went 'phwoof', he was very good wasn't he?
"It looked a slowly-run race and it looked nearly impossible to come from the back, so I will need to watch it again.
"Tom has given him a peach, because I didn't think it was being run to suit him at halfway because they went steady and I really got excited for El Drama who had a lovely spot with two to run.
"He was 33/1, so I'm not going to say he was going to win, but we thought he was a lively horse - he had very good juvenile form, but lost his way on the firm ground.
"In the French Guineas he was drawn wide in the car park, Goodwood he didn't really enjoy the Thoroughbred Stakes coming down the hill on very firm ground.
"I am delighted for the owners, they have been very patient. With horses, usually if it is in there, if you wait, it will come.
"He has had to step up massively on the form of winning the Fortune Stakes at Sandown, but that was a confidence-boosting run and that showed he really enjoyed that soft ground."
Varian had earlier seen his St Leger winner Eldar Eldarov disappoint in the Long Distance Cup, and added: "I said to my team, it's a funny old game. Jaws were on the floor after Eldar Eldarov. We had high hopes for him today, and then this happened!"
Marquand said: "It was absolutely mega! This fella was a spare ride and usually when you get Group One spares, you are up against it. But Richard (Ryan, of joint-owners Teme Valley Stud) and Roger were really keen that the surface was going to help and obviously he came here on the back of getting his head in front, which does a horse's confidence a lot of good.
"It is fantastic to walk away from Champions Day with another winner, as obviously they are hard to come by.
"I was really worried to be honest. They were not going very quick and I was further back than I wanted to be, but he obviously enjoyed chasing them down and from the two there was never a moment where I didn't think he would get there."
On Inspiral's slow start, Frankie Dettori said: "I went in the stalls second-last, I must have been in there about 10 seconds, the gates opened and she didn't want to come out, it was one of those cigar moments.
"The whole field went, I found myself last on a filly that needs cover so I ended up behind some outsiders. They went slow, I tried to creep into the race but the race was done at the start.
"I don't know why she did it, it's the first time she's done it and she couldn't catch up. I knew being on the outside could be a problem, the slow pace was another problem but she's won two Group Ones, horses are not machines and sometimes they underperform."
John Gosden said: "She stood in the gate, got left and off a slow pace in soft ground you are never going to win from there."
Thady Gosden added: "She was slowly away, it turned into a sprint and when you are that far back in soft ground there's not much you can do really. She's OK afterwards so we'll see where we go from there.
"There's never been any sign of her doing it before, it's frustrating but there's not much we can do. Hopefully she'll be back next season, but we'll chat with the Thompson family."
Of the placed horses, Charlie Appleby said of Modern Games: "I'm pleased, Will (Buick) just said he's as tough as teak, but he couldn't get his feet out of the ground and even if the winner had come closer to him that might have helped. He's run a creditable race and he'll head to the Breeders' Cup now."
Ed Crisford said of Jadoomi: "He ran a blinder. He popped out of the stalls and it can be a hard place to lead and James (Doyle) said he was happy in front. The winner came out of nowhere, but he's run a cracker and we couldn't be happier.
"I think Keeneland (Breeders' Cup) will have to be considered, James said coming round a bend might play to his strengths so I think that will be his next step. He wants cut in the ground. A furlong out I thought we'd win, but it's another step up."