"But I was glad we could get the yellow ribbons to show some appreciation".
Northern Irishman Rory McIlroy battled inconsistent wedge play, his frustration eased by a holed bunker shot at the 17th, which helped him join South Korean Kim Si-woo three back.
"The hard part about this course is you can get off track pretty quick if you're not playing well", Thomas told CBS television.
Day crept to 12-under after three straight birdies from the 10th hole, only to drop five shots in the next five holes and shoot 73.
Tiger Woods, an eight-time victor at Firestone, finished 15 strokes back after a 73.
Perry had two eagles and eight birdies at a wet TPC Twin Cities and leads the PGA Tour Champions event by five shots over Glen Day.
After shooting three-over par in Round 3, Tiger Woods says he was fighting "everything" and that he didn't warm up well or hit the ball crisply.
The latter is certainly true, given his good form of late and his fondness for the course.
Justin Thomas tried valiantly to have Jarrod Lyle's yellow bucket hats shipped to OH so the world's best golfers could wear them during the WGG-Bridgestone Invitational.
Tiger Woods, Phil Mickelson Going Head-To-Head For $10 Million
The Ryder Cup is September 28-30, and any match that takes place between Woods and Mickelson would not occur prior to then. The match was first slated for early July, before falling through.
Jason Day, who threw away a chance to win the Bridgestone Invitational two years ago, had a 69 and was four shots behind.
Thomas' ninth title on the US Tour, and second this year, earned him $US1.7 million (NZ$2.5 million) and moved him up one spot on the rankings to world No 2.
His grandparents were both in attendance, and Thomas clearly wanted to win with them there.
"My grandpa is not emotional, but I hadn't seen him smile or be that happy, maybe ever". "To win on a golf course like this, a championship golf course and always against a very tough field, it just felt great".
Leishman is a shot back of countryman Day, with a 67 putting him in a share of fifth at nine under and well in contention. The World Series of Golf began in 1962, and it became an official PGA Tour event in 1976.
As for Firestone, it has been an unbelievable run for Woods at the course that will no longer be host for the tournament - it is moving to Memphis next year. The World Golf Championship instead will move to Memphis, Tennessee. Stanley closed with a 68.
Johnson, the world's No. 1 player who was coming off a victory in the Canadian Open last week, started the final round 10 shots behind and shot 29 on the front nine. He shot 69 for an easy four-stroke victory over fellow American Kyle Stanley, with Denmark's Thorbjorn Olesen and Dustin Johnson tied third.
McIlroy added a three-under 67 to his opening five-under 65 on Thursday, leaving him at eight under for the tournament and well-placed to make a weekend charge for the summit of the leaderboard.