Daniel Berger and Charley Hoffman hit the front with one round to go in the Franklin Templeton Shootout.
The pair's round of eight under par in the modified alternate shot format followed an opening 12-under scramble and took them one shot ahead at Tiburon Golf Club in Naples, Florida.
Their second-round score was matched by Jason Dufner and Brandt Snedeker, who joined first-round leaders Harris English and Matt Kuchar in second place. English and Kuchar, winners in 2013 and second last year, shot five under par for day two.
Billy Horschel and Hunter Mahan were a further two shots back on 17 under after a round of four under, with Graeme McDowell and Gary Woodland joined on 15 under by Cameron Tringale - last year's champion alongside Jason Day - and his new partner Camilo Villegas.
Charles Howell III/Rory Sabbatini and JB Holmes/Patrick Reed were 14 under, with Open champion Zach Johnson and his partner Patrick Rodgers a further shot back.
Sean O'Hair/Mike Weir and Kenny Perry/Steve Stricker were 12 under and Retief Goosen and Danny Lee brought up the rear on nine under, having shot only level par and failed to advance from their first-round total of nine under.