AUGUSTA, Ga. — Dustin Johnson knew this wasn’t going to be easy.

Three days of practice rounds on the hard-and-fast fairways and greens at Augusta National made it pretty clear entering Thursday’s opening round of 85th Masters that the record 20-under-par winning score he posted in November wasn’t going to be attainable.

That didn’t make the 2-over-par 74 Johnson posted Thursday in defense of his title any easier to swallow.

“Yeah, the conditions are definitely different,’’ said Johnson, who trails first-round leader Justin Rose by nine strokes. “The course is a little bit firmer and faster. Playing definitely a lot tougher just because, when the greens are firm and fast here, the golf course plays difficult. Then you add the wind in today [and] it made it play really difficult.’’

Johnson had his round in red numbers, getting to 1-under par through 14, but a bogey on the par-5 15th and a double on the 18th left him 2-over for the day.

Only three players in Masters history have repeated, the last being Tiger Woods in 2001.

Brooks Koepka, playing three weeks after having surgery on his right knee, shot a 2-over-par 74 Thursday.

He said the knee was “fine,’’ adding, “I just didn’t play good. I just didn’t swing it great. It’s tired right now, I’m not going to lie. But [I’ve] just got to play better.’’

Past champion Ian Woosnam strained his right groin muscle and managed to shoot 76 anyway.

“I did it the other day,’’ he said. “I’ve been here over the weekend, just trying to hit it further. It is a hard walk, and I’ve just pulled a muscle in the groin and the back. I was thinking of coming in after 11, [but] I was scoring quite well, you know?’’

Asked what the odds are that he’ll keep playing, Woosnam said, “Well, being that I’m stupid, I’ll most probably play, get out there, and if it is unplayable, I’ll just have to come in. I’m playing on one leg really, plus I haven’t had a scorecard in my hand for 18 months, so I was pretty damned pleased really.’’

Woosnam has been sidelined with a back injury for 18 months.

“He’s a phenom, one of the shortest guys that ever played professional golf at 5-4 at his peak. … He may be shrinking now, I don’t know,’’ said Berhard Langer of Woosnam. “Inch for inch, he probably hit the ball further than any human being you’ve ever seen, and with his boxing background, he was just very strong and had a good mind for the game, beautiful technique.

“He’s been a wonderful champion. He’s won lots of great tournaments all over the place, and I guess he just had back surgery about a year ago or something like that … so I hope he’s feeling good enough to come back and play some on the Champions Tour.’’