It was just reward for the Charlie Hills-trained speedster after finishing second to Blue Point in the previous two runnings of the Group One showpiece.
The 5-6 favourite broke smartly and was always travelling smoothly in the hands of Jim Crowley, who was completing a double after his earlier victory on Motakhayyel.
When Crowley pressed the button, Battaash put daylight between himself and his rivals to score as he liked. Equilateral grabbed second place on the line from Liberty Beach to give Hills the first two home.
Crowley said: "I had to hold him for two furlongs as he was on a bit of a going day today and wanting to charge off - my only concern was trying to get the fractions right on him as there was nothing quick enough to lead him. When the gates opened today, he was gone.
"Every time he wins it feels special, as when he wins he wins well. I was a bit worried the stiff uphill finish might find him out on his first run, but he's just a real superstar.
"He's won the big three now - the King's Stand, the Abbaye and the Nunthorpe. Hopefully he's not finished yet - I'm very grateful to be riding him."
Hills said: "He broke out of the stalls fantastic and Jim didn't have much choice but to go forward. He always looked in command and it is a real shame Sheikh Hamdan was not here to witness it, but it is great to finally win a King's Stand with him.
"You get slightly tense, obviously, but I've lived every emotion with him. We've been beaten in this race twice before, so three times I don't think I could have dealt with that. His ace card is pretty much from the two to the one and he gets horses off the bridle. He gets them all going while he is still cruising.
"He is a very hard horse to pass when he is like that. He is just an amazing horse. Everyone in the yard is so lucky to have a horse like him, he is a horse of a lifetime. Not just that, it's the character he has at home.
"I was watching the race where no one could see me - no cheering, just get the job done.
"It wasn't to me (concern not having a prep race) as he has always been pretty good first time out and if anything it might just have flattened him the last couple of years. Let's see next year if we come straight here or not. It would be fantastic to come here as a seven-year-old."
On future plans, Hills said: "I'd feel really proud if he won that race (King George Stakes at Goodwood) four times. That would really be a highlight this season if he was able to do that.
"At the moment I would say Goodwood would be where we go next and then York. After that we'll have to speak to Sheikh Hamdan and decide (where we go).
"Whether he goes there (Breeders' Cup) will be Sheikh Hamdan's decision. We'll have to see how he gets on in his next couple of races and I'm sure there'll be a discussion about it.
"He's not the biggest horse, but he does put an enormous effort in when he runs and we have to be conscious of that. Some of the times he produces are ridiculous, so he really does put his heart and soul into his races."
He added of Equilateral: "I always thought he would run a big race. He has always shown he is a very good horse. I know a lot of people have lost a lot of money on him over the years. He deserves a big one in time. At the end of the day he hasn't even won a Group race yet so we will try to find a Group Three if we can."
NAZEEF COMPLETES TREBLE FOR JIM CROWLEY
Nazeef completed a treble on the opening day of Royal Ascot for jockey Jim Crowley and owner-breeder Sheikh Hamdan Al Maktoum with a narrow victory in the Duke of Cambridge Stakes.
Having already landed the Buckingham Palace Handicap on Motakhayyel and guided the brilliant Battaash to Group One glory in the King’s Stand for his retaining owner, the former champion jockey jumped aboard 100-30 chance Nazeef for this Group Two over the straight mile.
Winner of her previous four starts for John Gosden, the daughter of Invincible Spirit was among the leading contenders and travelled kindly towards the rear of the field for much of the contest.
Just for a moment it appeared big outsider Invitational may have cut loose, but she ultimately weakened fairly quickly and Nazeef charged home under her in-form rider – just getting the better of Agincourt by a head in a driving finish.
Queen Power, the 3-1 joint-favourite along with the bitterly disappointing Jubiloso, was best of the rest in third.
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