Putnam went even better, wielding a hot putter for a 64 to join Johnson at 15-under 195, the duo five shots clear of Stewart Cink (64).
"It feels like it's been a long time (since my last win), even though it's only been six months".
Johnson added a third round of 65 to his opening rounds of 67 and 63 but it was still not enough to hold off Putnam who is looking for his first PGA Tour title while Johnson has 17 titles to his name, one of those a major. The best U.S. Open finish by a victor of the St. Jude in the same year was a tie for third by Fred Couples in 1993, when the event was conducted two weeks before the Open.
The win also vaults Johnson to the new World No. 1. Instead, he rolled in the putt to keep his lead, and birdied the 13th to increase it to three. "I like this golf course, and I feel like I play it well and wanted to be on top of my game going into next week, too". Now he will play in the last group on the final day for the first time on the PGA Tour with Johnson.
Johnson finished with a flourish when his 171-yard second shot on the par-four 18th found the bottom of the cup, sending the crowd at the TPC Southwind in Memphis into a frenzy on a sweltering day. I'm hitting my irons well, and my wedges are really good.
"I have high expectations going in every week", Johnson said. He holed out from the right front bunker for birdie on the par-5 No. 16.
Putnam, 29, is a two-time Web.com Tour victor in his second full season on the PGA Tour.
"It obviously went pretty well", said Snedeker, the 2012 FedExCup champ. "You don't have them very often out here where the hole looks like it's the size of a beach ball and can't miss a putt".
Putnam, a two-time victor on the Web.com Tour, had only one bogey through his first three rounds. John Daly withdrew before the second round. Scott Piercy withdrew after nine holes at 5 over.
In a final walkthrough before heading off to Shinnecock Hills and the Open, Dustin Johnson sauntered to a six-stroke victory in the FedEx St. Jude Classic on Sunday to reclaim from Justin Thomas No. 1 in the World Golf Ranking. And from that moment on, Johnson's second title of 2018 was never in doubt.