– Jason Day spent his first nine holes of the Masters walking gingerly, swinging carefully and walking behind trees to lay on a towel so his chiropractor could work on his ailing back.

He woke up on Friday morning, complained about the pain, and received a pep talk from his sports psychologist. Or a rebuke from his wife. Phrase it however you like.

“My wife, Ellie, I looked at her, and I was kind of moping a little bit in the bath, and she’s like, ‘It’s the Masters, you need to suck it up,’ ” Day said. “So I can’t complain about it too much. Because, I said earlier, that she’s birthed three children and I haven’t, so she’s a lot stronger as a person than me with regards to pain, and I just hit a little white golf ball around the course.”

Day bent down to kiss his daughter before the first round and felt something give in his back. “I said to my caddie, Luke, if this stays the same pain as it was on the putting green, I’ll probably end up withdrawing.”

Day looked gimpy on Thursday. Friday, he looked like the player who won the 2015 PGA Championship at Whistling Straits. He shot a 5-under-par 67 for a tie with four others at 7 under atop The Masters leaderboard.

Day is 31. Back injuries can make you feel multiples of your age.

“Sometimes I wake up and I feel like I’m 50, sometimes I wake up and feel like I’m 70, and sometimes I wake up and feel like I’m 18 again,” Day said. “It just comes and goes, and that’s just how it is.

“I’m trying to do everything I can to make sure that I have longevity in my game, and that’s something that I need to focus more on now than ever before, just strictly because I have to work harder than most guys, especially with a back injury.”

The old saying might apply: Beware the injured golfer. Swinging under control because of his back, Day made just one bogey on Thursday, and played the last six holes in 3 under.

Day has dealt with back pain since he was a teenager. He has to adjust his ribcage and pelvic floor — “This is my trainer talking, not me,” he said —and blows into balloons to get himself into alignment.

“It takes 20 or 30 minutes in the morning and 20 or 30 minutes at night,” he said. “And then I go see my chiro, and sometimes it’s 10 minutes and sometimes it’s 20 or 30 minutes, so there’s a good hour, and you obviously have to go out and warm up and make sure everything’s good.”

Beware the injured golfer.

Beware the golfer with the blunt wife.