Woods has 18 victories in that period, while Rory McIlroy also has 12.
Not that Johnson was thinking about his place among the elite as he recovered from a faltering start in the final round at Crooked Stick in Carmel.
It took him only three holes to give up his three-shot lead to Casey but four birdies in the next five holes re-established his advantage and he was never headed again.
The U.S. Open champion continued the best year of his career, carding 67 to finish at 23-under-par 265.
"I hit a lot of good shots, a couple of bad misses but other than that played really solid all week," Johnson, 32, said in a greenside interview.
"I got a lot of confidence in every part of my game, especially all the work I’ve put in on my wedges has really paid off this year, and this week I (used a) new putter and it really worked."
Englishman Casey also shot 67 for second place on 20 under, his second consecutive runner-up finish, with American Roberto Castro (67) another three shots back in third place. Johnson finished 11 strokes clear of fourth place.
With his third win of the year, Johnson jumped to top spot on a FedEx Cup points list as the top 30 players advance to the season finale Tour Championship in Atlanta in two weeks.
Among notables to fall outside the top 30 and miss out on a chance at the $10 million jackpot were American Rickie Fowler, Spaniard Sergio Garcia, American Brooks Koepka and Swede Henrik Stenson.
Fowler, who finished 59th in the 69-man field on Sunday, is among those hoping to be named on Monday among U.S. Ryder Cup captain Davis Love's three wildcard picks for this month's event against Europe.
Love will make his fourth and final pick after the Tour Championship.
Johnson said he was "frustrated" by his poor start to the final round -- bogeying the second and third holes -- but was confident he was playing well enough to turn it around in his 200th start on tour.
"I hit a couple of squirrelly shots there," he said. "It was nice to make a birdie on four ... and then hit some really nice wedge shots after the first few holes."
World number one Jason Day withdrew on the ninth hole with what his agent described as "a pinched joint in his lower back capsule with muscle spasm."
(Reporting by Andrew Both in Cary, North Carolina; Editing by Clare Fallon / Ian Ransom)
