Phil Mickelson, a two-time victor at TPC River Highlands who held the 36-hole lead, carded a second straight 71 to finish in a tie for 24th that included seventh-ranked Patrick Reed, who posted a 64, while second-ranked Jon Rahm of Spain totaled 71 to tie for 37th, and defending champion Chez Reavie tied for 46th with a 69.
Former US Open champion Johnson has now collected 21 PGA Tour titles, and at least one every year since 2008, a record he was proud and relieved to have continued in CT after a barren run of results over the last few months.
He concluded at 19-less than 261 for his 21st PGA Tour title.
Out of the break, Johnson finished bogey-par-par to win by one.
A delay for lightning could not derail Dustin Johnson as he secured victory at the Travelers Championship for his first win on the PGA Tour in 16 months. I'm definitely proud of myself for continuing the streak, and I want to keep it going, but it was a long time between wins.
His ball buried deep in the bank of a bunker, Todd shanked his pitch and then came up short with an ambitious flop-shot before a putt up the slope also lacked the pace to reach the putting surface.
He made par, only to bogey on the next hole, after rain forced a brief delay.
Johnson resisted the urge to play cautiously and hammered his final drive over 350 yards down the fairway, flicked a wedge to the heart of the green and two-putted for the winning par and a one-shot victory over Streelman, with Will Gordon (64) and Mackenzie Hughes (67) sharing third on 17 under.
"I've had a few missed cuts, so to come back and finish a solo second is nice, but to be that close and perform and be right there, I'm just a little disappointed right now", Streelman said.
Gordon, who had no status on either the PGA Tour or the Korn Ferry Tour, had seven birdies in a 64. He finished the round with a much straighter 43-foot birdie putt on 18. The finish was just enough to give him a special temporary card and unlimited exemptions for the rest of the season.
Johnson was tied for 79th after the opening round on Thursday, the lowest first-round position by a victor in the tournament's history. He looked to have taken an unassailable grip on the lead when Todd, who opened with 11 consecutive pars, fell out of contention at the 12th.
His five-over 75 left him a share of 11th in a group that included world No.1 Rory McIlroy (67).
The PGA Tour is making some tweaks to its coronavirus policies as a result of this week's issues.
Global COVID-19 death toll cross 5 million
US Secretary of Health and Human Services Alex Azar described the current situation as "very serious" during his TV appearances. The United States has suffered the highest death count (125,803), followed by Brazil (57,622) and the United Kingdom (43,634).