PORTRUSH, Northern Ireland — Irish eyes are smiling.

Irish eyes are crying.

Tears of joy and disbelief.

Can it be that an Irishman has won the British Open at Royal Portrush the first time the oldest and most prestigious championship has been played in Ireland in 68 years?

Indeed, the historic week converged into the perfect storm for the proud nation on Sunday when Irishman Shane Lowry hoisted the Claret Jug as the “Champion Golfer of the Year’’ with a stout, runaway performance in some grueling conditions.

Lowry, who took a four-shot lead over Englishman Tommy Fleetwood into the final round, won by six shots after shooting a 1-over 72 Sunday to finish 15-under for the week. Fleetwood finished second at 9-under, Tony Finau third at 7-under and Brooks Koepka and Lee Westwood tied for fourth at 6-under.

It was a result that stunned even the 32-year-old Lowry.

As he walked down the 18th fairway with his insurmountable lead and the thousands of fans in the grandstands and pressed against the ropes and barricades on either side of the fairway singing, “Ole, Ole, Ole, Ole,’’ Lowry said to his caddie, Bo Martin, “I can’t believe this is happening to me.

“I suppose I didn’t even know going out [Sunday] morning if I was good enough to win a major,’’ Lowry said afterward. “I knew I was able to put a few days together. I knew I was able to play the golf course. And look: I’m here now, a major champion. I can’t believe I’m saying it, to be honest.

“I kept on telling [Martin] how nervous I was, how scared I was, how much I didn’t want to mess it up. All I could think about was walking down 18 with a four- or five-shot lead. And lucky I got to do that.’’

Lowry had missed the cut in the last four Open Championships, the most recent last year at Carnoustie, where he shot 5-over and went home early.

“I sat in the car park in Carnoustie almost a year ago right to this week and I cried,’’ Lowry said. “Golf wasn’t my friend at the time. It was something that had become very stressful and it was weighing on me and I just didn’t like doing it. That just shows how fickle golf is. Golf is a weird sport and you never know what’s around the corner.’’

Sunday was never going to be easy for Lowry. Leading a major championship entering the final round never is for anyone, Tiger Woods and Jack Nicklaus included.

Especially when you’re trying to win your first.

Especially when you’re trying to do it in your home country.

Especially when tournament officials were so unnerved by the gnarly weather forecast they did something they rarely do: move the tee times up a couple hours.

“So Shane’s in the lead; he’s got a big lead,’’ Westwood observed before the final round. “But no lead is big enough when the weather gets back on links course.’’

Lowry knew how treacherous the task was ahead of him. He knew it, and so did everybody else.

“He’s going to have an awful lot of pressure on him from the crowd,’’ Westwood said. “He’ll be nervous. It’ll be a tough, long day for him. Last day is always long, but it’s going to be 100 times worse for him.’’

Lowry wobbled right away, hitting what he described as a “ropey’’ tee shot off the first into some heavy rough, then hitting into a green-side bunker short, splashing out and leaving himself a nervy 6-foot bogey putt.

Fleetwood, meanwhile, had an 8-footer for birdie. A possible two-shot swing on the first hole looked possible. But Fleetwood missed his birdie putt and Lowry drained the bogey putt and walked to the second tee having lost only one shot.

“When he holed that putt for bogey on the first, I’m sure he walked to the second tee feeling like he’d won the first hole,’’ said fellow Irishman Padraig Harrington, who waited for Lowry on the 18th green to congratulate him.

“That,’’ Lowry said of losing only the one shot on No. 1, “settled me an awful lot.’’

From there, even with torrential rain and winds that gusted to 35-40 mph in the middle of the round, Lowry never wavered.

“He literally controlled the tournament from the start of the day until the end, and that’s a very, very impressive thing to do,’’ Fleetwood marveled.

“Props to Shane,’’ Koepka said. “To shoot 1-over with the lead, with these conditions, that’s unbelievable. How cool is that to win in Ireland?’’

So cool that those Irish eyes were probably bloodshot Monday from all the celebration on Sunday night.