PALM BEACH GARDENS, Florida — So, what’s the perfect way to savor a round of golf so extraordinary that it goes down in history? For Jake Knapp, the answer was simple: Head straight to the putting green for more practice.

“Always,” Mr. Knapp told The New York Sun about his habit of grinding away. “You can always get better.”

His performance on Thursday defied belief. On a picture-perfect day with nary a breeze to defend PGA National, Mr. Knapp buried a one-footer for birdie at the par-5 18th hole to put him at 12-under for the day. It marked just the sixth time in PGA history that anyone has shot that score in one round.

“It was definitely one of those days where I just tried to get out of my own way,” Mr. Knapp told the Sun while heading to the practice green. “I knew I was hitting the ball well, so I just needed to go trust that and keep the pedal down.”

His putter was red-hot in totaling 12 birdies, and his ball-striking was consistently accurate. He made birdies on his first five holes, including a chip-in on the second. After posting a 29 on the front nine, he birdied five of the first six on the back before arriving at the 18th, where an eagle putt from 18 feet, 8 inches would have earned him a 58.  His roll stopped a foot short, leaving the easy birdie for the 59.

“My initial thought was, ‘Don’t do anything stupid,’” Mr. Knapp told the Sun of his approach at the 18th. “I know it’s a hole I really like. It would have been nice to hit a more aggressive putt for 58, but I wasn’t going to do anything silly. I took the 59 and ran.”

Mr. Knapp, 30, earned his first Tour win at last year’s Mexico Open. It was one of four top ten finishes in a season during which he secured his PGA Tour card, earned a spot in the Masters, and took home more than $3 million in prize money. The Cognizant is his seventh appearance this year.  He has made six cuts, but is looking for his first top ten finish.

Three sub-70 rounds at the Mexico Open last week offered signs of a positive trend, but the career round was stunning.  “I don’t know if you ever feel a round like that coming,” Mr. Knapp said, “but I definitely feel like over the last couple of months it’s slowly been getting better. To be honest, I started to hit the ball well at Pebble [Beach] and Waste [Management]. I just couldn’t keep it going for four days or over the course of different weeks.  But last week at Mexico, I was no. 1 in ball striking on Sunday and felt I was hitting the ball a lot better and just tried to continue those feels this week.”

Mr. Knapp is among a group of young golfers emerging on the PGA Tour while top-ranked players such as Scottie Schefter and Xander Schauffele deal with health issues. While some familiar names, such as Hideki Matsuyama (The Sentry) and Rory McIlroy (Pebble Beach), have claimed victories this year, newcomers like Nick Taylor (Sony), Ludvig Aberg (Genesis), and Belgium’s first winner, Thomas Detry (Waste Management), also have stepped into the winner’s spotlight.

There is plenty of attention this week on Luke Clanton, the no. 1-ranked amateur, who needs to make the cut to secure his PGA Tour card.  The Florida State Seminole and native of nearby Hialeah, Florida, said he has played PGA National about 40 times and he put the local knowledge to good use, shooting an opening round 4-under 67.  He needs 20 points to earn his Tour card through the PGA Tour University Accelerated program. He currently has 19 and would earn a valuable point by making the cut.

Conditions were perfect for scoring on Thursday, with temperatures in the mid-70s and virtually no breeze on the course. Mr. Knapp finished tied for fourth here last year, and expects good things for the rest of the weekend. “I like this golf course a lot,” he said. “It fits my eye. There are some tough tee shots and what not, but for the most part the course is really good for me. I enjoy playing it.  I definitely had some good memories coming back here.”

He made more good memories on Thursday.