PORTRUSH, Northern Ireland — The challengers have no choice on Sunday but to challenge on what figures to be a challenging day for all involved.

Make no mistake: The 148th British Open is Shane Lowry’s to win. After a brilliant 8-under 63 he shot in Saturday’s third round at Royal Portrush to set the tournament 54-hole record of 197, Lowry takes a four-shot lead into Sunday’s final round.

If this is going to be a race down the back nine with drama, it’ll be up to Tommy Fleetwood, J.B. Holmes, Brooks Koepka, Justin Rose, Rickie Fowler, Lee Westwood and possibly a few others to make Lowry sweat as he tries to win his first career major championship.

Fleetwood, who shot a 5-under 66 without a single bogey on Saturday and still lost ground on the scalding-hot Lowry, is the nearest challenger at 12-under, four shots back. Holmes, who played with Lowry and shot a respectable 69 Saturday, is 10-under, four shots back.

Koepka, who shot 67 and has been lurking all week despite an icy-cold putter, is 9-under, five shots back, as is Rose, who shot 68. Fowler (66) and Westwood (70), the two best players never to win a major, are eight shots behind at 8-under.

Of those players, Koepka, with major championship victories in four of his past nine starts, is the hottest player in the world and possibly the man for Lowry to fear most.

“Nobody has hit it better than me this week,’’ Koepka said. “I’ve hit it as good as I could possibly imagine. I putted the worst in the entire field, if you look at strokes gained. It’s been really bad. Very frustrating. Disappointed.

“But thankfully, it’s going to blow [Sunday]. To have any sort of chance, I need to figure out the putter.’’

Ah, yes, the weather.

The forever unpredictable Irish weather is forecast to be so poor late Sunday afternoon that tournament officials moved the final-round tee times up some 90 minutes with hopes of getting the tournament in. The lead group — Lowry and Fleetwood — will tee off at 1:47 p.m. local time, 8:47 a.m. Eastern.

“It’s the best golfers in the world. I feel like the guys that are up there on the leaderboard, from what I’ve seen, are not going to be too fussed about the conditions,’’ Fleetwood said. “It’s not like it’s an advantage or disadvantage to anyone. I personally don’t mind the conditions, whatever they are. I feel like I’ve had some of my best rounds in terrible, terrible conditions, where I’ve enjoyed grinding it out. So we’ll see.”

Rain is forecast for most of the day with winds around 20 mph — with gusts near 40 mph possible.

“Shane is definitely … he’s not played in sunshine and no wind all his life,’’ Fleetwood said. “So it’s not going to be a problem for him, either. It’s just another added script to the Open, really, the weather, which is always part of it. Maybe the weather will play a part in that.

“Put it this way, it will be a very, very good effort if it’s me, and if it’s not me or Shane, it will be a very, very good effort for somebody else. For sure, we’ll see how it goes.’’

Koepka said he’ll welcome the poor weather. The worse the better as far as he’s concerned.

“I need it,’’ he said. “Being seven back, you need some wind, you need some rain, you need anything that can kind of go your way. And that’s got to be an advantage — especially the way I’m striking the ball. I’ve struck it so good. If it’s going to be windy, you need to be able to strike it good, control your flight, and figure out where you want the ball to end up. If it’s going to blow 30 [mph], it can get out of control very quickly.’’

Koepka, perhaps bringing in a little bit of mind games, brought up Lowry’s lost lead in the final round of the 2016 U.S. Open at Oakmont, where Lowry was overtaken by Dustin Johnson. Koepka also referenced himself nearly losing a seven-shot lead in the PGA Championship at Bethpage in May.

“The last time Shane had the lead at Oakmont we saw that,’’ Koepka said. “At Bethpage, it can go very quickly. Bad weather happened at Bethpage. I guess maybe the last, what, 15 holes was very, very windy, especially that back nine. In links golf, all of a sudden a couple of bad bounces and you never know or in a couple of bunkers.’’

Said Holmes: “It’s tough no matter whether you have a one-shot lead or five-shot lead. It’s tough to finish off a major. It’s a tough test. So we’ll see. See what [Lowry] does [Sunday].’’