Although he currently resides and trains in California, O’Callaghan was born in Clare and has trained in America since 1990, working for the likes of Todd Pletcher.
His 7-1 chance travelled strongly throughout the six-furlong contest under Garrett Gomez and quickened to the front in the straight.
Hot favourite Rocket Man was making ground all the way to the line but Kinsale King kept responding to his rider’s urgings to take Group One glory.
His jovial trainer, also a part-time pub singer in south Los Angeles, now has his sights set firmly on a trip to Royal Ascot in June.
He said: “I’m Irish through and through, as are the owners who are from Kinsale and that’s how the horse got his name.
“He’s always proved he’s a grinder from whatever position he’s been in.
“We’d done all of our homework and I wasn’t too worried about the opposition – I only concentrate on my horses.
“I wasn’t watching Rocket Man at the finish, it was my own rocket man I was looking at.
“I knew he had won when I put the saddle on and the race went exactly like I wanted it to.
“To win here is amazing and is what I always wanted to do with my life. I’ve now proved I can do it and hopefully it will open more doors.
“We’ll be off to Royal Ascot next for the Golden Jubilee.”
The runner-up could also be Ascot-bound. His trainer Patrick Shaw said: “We’ll see how he pulls out but Royal Ascot is a possibility and the track there would suit him.”
Al Shemali sprung a huge surprise when landing the Dubai Duty Free at Meydan under Royston Ffrench.
The six-year-old was sent off at 40-1 for the Group One contest but while a number of strong closers such as Luca Cumani’s market leader Presvis failed to get a run, Al Shemali had already kicked for home halfway up the straight and passed the post nicely clear of Bankable.
Cumani said: “That is horse-racing for you. In a 16-runner race with a short straight, things like that are always going to happen.
“If we’d gone for the Sheema Classic, we would have had an extra three furlongs to recover but if you get blocked over this trip, that is it.
“He was travelling strongly when it happened and was still on the bridle, but got put in prison.
“He’s not had a hard race and will often do more in a gallop.
“We’ll take him back to Hong Kong now.”
There was a dream start to Mahmoud Al Zarooni’s career as an official trainer for Godolphin as his first runner Calming Influence (14-1) landed the Godolphin Mile.
Godolphin racing manager Simon Crisford said: “He’s always been a nice horse and this victory is not a surprise.
“To have Mahmoud winning with his first runner is huge.
“Sheikh Mohammed has put his trust and faith in him and to start with a winner here at Meydan is very special.”