Shane Lowry is also facing an uphill battle after a second-round 72 left the Offaly native one-over-par.
Rory McIlroy remains well off the pace at the FedEx St. Jude Championship after a second-round 70 left the Holywood golfer on four-over-par in Memphis.
The world number three improved on his opening round, with birdies at the third, fourth and tenth, but late bogeys on the 17th and 18th saw him slip further down the leaderboard.
Meanwhile, world number one Scottie Scheffler stormed into the outright lead after carding a brilliant nine-under-par 61 to move to 11-under overall.
Shane Lowry is also facing an uphill battle after a second-round 72 left the Offaly native one-over-par, with a difficult closing stretch dropping him back into the middle of the field.

Wales Stun All Blacks To End 73-Year Wait For Victory
Ireland Face Must-Win Kosovo Clash After Narrow Defeat To Austria
Kildare Trio Feature As Ireland Overcome Fiji In Nations Championship
Kildare's Sean O'Haire Kicks Dramatic Last-Minute Winner In American College Football
Sunday Morning Sports Update
Milltown Through To Leinster Intermediate Semi-Finals After Victory Over Meath Champions
Sarsfields Leinster Championship Campaign Ends After Heavy Defeat To Cuala
More Than 20 Horses Withdrawn At Cheltenham Over Ground Conditions