Johnson fired a six-under par 65 to finish the 54 hole event on 19-under.
Kuchar (68) was one ahead of joint third place getters Vijay Singh (68) (the Fijian is now a chance to grab a spot on the Presidents Cup International team) and Brandt Snedeker, who fired a final-round 61.
Jason Day (66) and Aaron Baddeley (69) were the best placed Australians, finishing tied for 10th on 12-under.
The top 100 in the cup table will move on to the second event in the US PGA Tour playoff series, The Deutsche Bank Championship in Massachusetts, beginning early Friday Australian time.
That playoff will include Day and Baddeley as well as fellow Aussies Adam Scott, Robert Allenby, John Senden, Marc Leishman, Geoff Ogilvy and Greg Chalmers.
Dropping out of the race for the US$10 million Fedex Cup first prize this week were Australians Nick O’Hern, Stuart Appleby, Rod Pampling and Steve Bowditch.2011 The Barclays Final Results 2011 FedEx Cup Standings