Johnson hit his drive into the left hazard on No. 4 at the Kapalua Plantation Course and proceeded to hit his second shot from inside the red stakes after a volunteer marshal pointed out where the ball was.
Only after he hit it did Johnson realize that the ball wasn't his, and by hitting the wrong ball, he was slapped with a two-stroke penalty under Rule 6.3. DJ's actual ball was 10 yards farther, slightly inside the hazard line.
"The marshal had it marked, said it went in the hazard right there and there was a ball right there and it was a Taylormade," Johnson said after his round. "I just assumed it was mine and it was way up in the air, so I didn't want to move anything."
However, the new rules state that a player can identify their ball in a hazard without penalty even if it moves.
Ironically, the infraction occurred a day after the 34-year-old admitted he hadn't studied the newest rules thoroughly and neither had his caddie and brother, Austin.
"That won't ever happen again, I can promise you," Johnson added with a smile.
He went on to make double-bogey on the hole instead of a par.