With only the top two gaining automatic promotion to the riches of the Premier League, Sean Dyche's Burnley moved a point clear of Middlesbrough and three ahead of third-placed Brighton & Hove Albion.
Middlesbrough, who have a game in hand, can regain top spot in the second tier table when they host Ipswich on Saturday, and Brighton, who have also played a game fewer than Burnley, are away at relegated Charlton.
Barton scored the only goal after six minutes when his curling free kick cannoned off the wall and wrong-footed Preston keeper Chris Kirkland on its way into the net.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Burnley, who have two matches left in the season, could have extended their lead in the second half when they hit the woodwork twice in quick succession.
Andre Gray's effort hit the post and George Boyd clipped the top of the crossbar with a shot from distance as Burnley extended their unbeaten league record to 21 matches.
(Reporting by Toby Davis; editing by Ed Osmond)
