Jon Rahm walked off the 18th green at the Memorial after tying the 54-hole record and building a six-shot lead, leaving him on the cusp of joining Tiger Woods as the only repeat winners.

Moments later, he doubled over behind the green and said in anguish, “Not again!”

Rahm had just been notified he had tested positive for the coronavirus, knocking him out of the tournament.

“This is one of those things that happens in life, one of those moments where how we respond to a setback defines us as people,” Rahm later posted to Twitter.

A commanding performance, that included a hole-in-one Saturday morning to complete his second round and an eight-under 64 to tie two tournament records, went to waste.

The PGA Tour said the Spaniard had come in close contact with a person who was COVID-19 positive, meaning he could play provided he was tested daily. Every test came back negative except the one after his second round, which was completed Saturday morning.

The positive test was confirmed, the results returned as he was playing the 18th hole, knowing nothing except no one was close to him on the leaderboard.

“I feel very bad for Jon Rahm. He’s played absolutely brilliant golf this week,” tournament founder Jack Nicklaus said on social media.

“Our hearts go out to Jon and his family, as well as all the patrons who witnessed a spectacular round … only to be negated by this horrible pandemic our world continues to endure.”

Sorry, but that’s the rule

By tour policy, he was withdrawn from the Memorial leaving Patrick Cantlay and Collin Morikawa tied for the lead at 12-under.

“It’s kind of the worst situation for something like that to happen and he played awesome today and it’s just, it’s really a shame,” Cantlay said.

Rahm, who remains asymptomatic, was close to perfect on the back nine, running off six birdies in an eight-hole stretch to turn a one-shot lead into a six-shot cushion, tying the Memorial record for largest 54-hole lead set by Woods in 2000.

His 18-under 198 tied the record set by Scott Hoch in 1987.

The world No.3 is required to go into self-isolation for 10 days. That ends on June 15, the Tuesday of the US Open at Torrey Pines, where Rahm captured his first PGA Tour victory four years ago.

Rahm was the fourth player to test positive during a tournament since the tour returned to competition one year ago in Texas.

Cantlay and Scottie Scheffler, who played with him in the third round, both said they already have had the coronavirus.

Scheffler didn’t see Rahm behind the green and wasn’t sure what was going on when he walked into the scoring room to sign his card. He said Rahm looked frustrated.

“He just goes, ‘Good luck tomorrow,’ and I’m like, ‘Thanks, man. You play good, too.’ I was just really confused,” Scheffler said.

“He’s like, ‘No, man, I just tested positive.’ My heart just sank. It’s terrible that happened.”

With a victory, Rahm could have moved closer to recapturing the world No.1 position, along with earning over $US1.67 million ($A2.1m).

-AAP