American Marc Turnesa regained the lead in the Shriners Hospitals for Children Open but compatriot Chris DiMarco put in the best performance to move into contention with a day to go.

DiMarco carded a round of 63 to leap to 20-under, one behind Turnesa who shot 69 in his third round at TPC Summerlin in Las Vegas.

Former Masters champion Zach Johnson is just two off the lead after a round of 70, while Londoner Brian Davis carded a 66 to be a further two strokes behind.

Kenneth Ferrie's struggles continued as his 70 left him 10 under for the tournament in a share of 52nd.