Up to 40 members of the Rathmore Golf Club, where he learnt to play, stayed up all night to cheer him to victory at the clubhouse and few had been able to grab more than a few hours sleep.
His uncle Uel Loughery, who coached Graeme as a youngster, was among those who stayed up.
Mr Loughery said: “He first picked up a club when he was nine. He started playing with his brother Gary. A deal was done with Dai Stevenson — the old pro at Portrush — so that they could play on Saturday and a couple of nights a week.
“I started coaching and he was playing off a 35 handicap then, but by the age of 14 he was playing off two.
“He always had a great temperament for the game. I kept coaching him until a few years ago when he was about 25 and had won his first couple of tournaments.”
Mr Loughrey added: “I was no more than an amateur but I got more enjoyment from coaching than playing.
“I started work at 5am this morning so I haven't been to bed yet. He rang me at 5.30am and said he'd be back soon and he'd be buying me a pint.”
Another who got little sleep was Rathmore club captain Colin Walker. He said: “I didn't sleep much last night because I didn't know what was going to happen today.
“We are all very proud, it is an unbelievable achievement.”
Mr Walker said an emergency meeting of the club would be called to decide how best to welcome McDowell home.
Club member Paddy Coulson said: “I don't know how you would describe it. It's just great to see that he has won a Major title.”
Coleraine mayor Norman Hollis, also a Rathmore member, said: “It's a big moment for Northern Ireland but as the mayor of the Borough of Coleraine I think it’s fantastic and the fact that he is Portrush-born and bred and that he learnt his craft here at Rathmore is just brilliant.
“We, the people of Portrush, are immensely proud of his achievement and on behalf of everybody here I would like to send out best wishes to his mother Marion and father Kenny.”
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