American Justin Thomas has maintained his lead at the John Deere Classic in Illinois with a second-round 67 to finish the day on 12-under-par.

With a first-round 63 apiece, Thomas and Nicholas Thompson brought the overnight lead into Friday's session, and five birdies for the former saw him retain that advantage heading into the weekend.

Thompson endured a trying second round, however, carding 72 to finish five strokes off the pace.

Johnson Wagner shot 63 to propel himself into contention as the American sits one shot behind Thomas on 11-under, alongside Tom Gillis, who carded 65.

Zach Johnson, who goes to St Andrews for The Open next week looking for a second Major title, finished the day on eight-under.

Jordan Spieth, favourite to win the Claret Jug in Scotland, improved on his first-round 71 by recording a 64 to finish on seven-under.