The long-hitting American, who was dealt a cruel blow when he narrowly missed out on joining a playoff for the 2010 Championship, fired a sparkling five-under-par 65 to post a two-under tally of 208.
In dazzling sunshine at Oak Hill Country Club where the par-70 East Course was beginning to run fast and firm after being rain-softened earlier in the week, he piled up six birdies and a lone bogey to finish seven strokes off the overnight lead.
"I felt like I played a lot better than my score was for the first couple of days," he told reporters, referring to his opening rounds of 72 and 71.
"Today I hit it really well. The only bogey I made was on number five and that was from the fairway. But I had a mud ball. Just kind of shot it up to the right and actually hit a good pitch and missed a short putt.
"I rolled the putter really well and just gave myself a lot of opportunities to make birdie."
Johnson, who was famously eliminated from the playoff at Whistling Straits in 2010 after being handed a two-stroke penalty for grounding his club in a bunker, relished playing early on smooth greens in the third round.
"This morning the greens were perfect, couldn't ask for any better," said the 29-year-old, who had been a distant 12 strokes off the pace overnight. "Obviously with no rain they weren't quite as soft, which was nice.
"Yesterday afternoon they got a little bumpy, but with the rain and 160 guys walking on them, they are going to get bumpy. Just something you have got to deal with it. This morning we went out and the greens were absolutely perfect."
A seven-times winner on the PGA Tour, Johnson felt that course conditions were likely to become even more difficult for the leaders during the afternoon as the course dried out even more.
"I thought it was playing pretty tough out there and I played really well today," he said. "I drove it well, drove it in the fairway and made some good putts.
"If this wind picks up, even par will be a good score, I think. You've just got to try to hit the fairways and get it on the green and get a look at birdie."
(Reporting by Mark Lamport-Stokes; Editing by Julian Linden)
