Ryan Blaum and Andrew Putnam each shot 64 and were tied for second, and C.T. Pan (65) and Wesley Bryan (66) followed at 8 under.
"I feel my game is really good, really solid", said Pan, a former University of Washington star now in his second year on the Tour.
Johnson and Putnam were tied for the lead at 15 under after the third round and were five strokes clear of the rest of the field.
Cook's 5 under on Sunday tied him with Phil Mickelson and Tim Herron for the best scores of the final round and moved him up the leaderboard into a tie for sixth.
The win ensures Johnson will return to the top of the rankings as the golf world prepares for the second major of the season at next week's US Open at Shinnecock Hills, New York.
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Both Albania and Macedonia hope to launch full membership negotiations with the European Union. Tsipras says the name would be used by the country both domestically and internationally.
Johnson birdied the third hole and bogeyed the fifth to make the turn at even par. He wound up three-putting for double bogey. "I've got a lot of control of my golf ball and that's what you're looking for going into any week, but yeah, especially going into [Sunday] and then obviously next week".
"Just wanted to play, stay sharp", Johnson said.
"When you're around or in the lead you can definitely feel the pressure but I like it", Johnson, 33, said. "Normally you have to drive it really well to succeed here but my iron shots have been good when I've been in the fairway and I've managed myself out of the rough really well".
Langer closed the bogey-free round with a 12-foot birdie putt on the par-4 18th at Wakonda Club.
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Guillem Balague says Julen Lopetegui's appointment as Real Madrid manager came as a surprise, but insists fans will be happy. Tottenham boss Mauricio Pochettino has been linked with the Bernabeu post but they have agreed a deal with Lopetegui.
He previewed his dramatic finish on the par-5 16th.
Johnson holed out a sand wedge from 111 yards on the par-4 No. 1 for eagle and almost holed out again on No. 2 from 114 yards, tapping in from 9 inches for birdie.
Snedeker, who lives in Nashville, Tennessee, hadn't played this event three hours away from his home in five years and none of his eight PGA Tour victories have been at the TPC Southwind.
He holed out for eagle from 170 yards on the final hole to seal an emphatic six-stroke victory at the St. Jude Classic.
Spain manager Julen Lopetegui announced as Real coach
They also scored 36 goals, and their form means they are one of the favourites ahead of the tournament in Russian Federation . It remains to be seen if he will head to Real as a World Cup victor , though Spain's squad is stocked with exciting talent.