The 10-1 chance, trained by James Fanshawe, took his first victory since the Golden Jubilee Stakes at Royal Ascot in 2011.
"He travelled really well and I got all the splits down the rail that I needed," said Fallon.
"He's a little terrier and he tries very hard, which is what you need in this type of race.
"I followed James [Doyle, riding Bated Breath] through as I thought he was the horse I had to beat, he gave me a lovely lead through and I was able to pick up on that fast ground.
"I've never won this race before, so it was nice. I want to get as many Group Ones as I can."
Fanshawe said: "It's been a real team effort - I just felt he was a very underrated horse.
"We've been really working on him in the stalls since the July Cup and it's paid off today.
"I haven't had a winner at Haydock in about three years, and I thought with the ground a bit quick and the stalls that we had no chance. I'm chuffed for the horse, the owner and the yard.
"I'm looking forward to the Qipco Champions Sprint at Ascot in October. This is the second Group One he has won and he is a proper horse. If we had got his stalls problem organised a bit earlier, I'm sure his record would have been even better.
"He completely missed the break when he was fifth in this year's Golden Jubilee. He's always hovered there in these big sprint races.
"I was very worried about the ground. I think Haydock is like Ascot. It is better to ride than to walk because it has got that cushion underneath.
"We were thinking about pulling him out at one stage but I'm glad we didn't."
Gordon Lord Byron was second, three-quarters-of-a-length back, despite a late charge.
Bated Breath was third while favourite Ortensia's winning streak of two came to an end, finishing 12th of the 13 runners.
She was later shown to have been cut above the sesamoid bone on her front leg, finishing her European season.