Miami - Matt Kuchar and Harris English fired a combined six-under-par 66 on Friday to take a one-shot lead in the Franklin Templeton Shootout pairs event in Florida.
Kuchar and English moved to 21 under after two rounds, one clear of Steve Stricker and Jerry Kelly who carded a four-under-par combined 68 in the modified alternate shot format at Tiburon Golf Club.
Kuchar and English's round sets up an intriguing final day battle in Saturday's better ball.
Harris and Rio Olympics bronze medallist Kuchar won the event in their first start together in 2013 and finished as runners up in 2014 and 2015.
Kelly and Stricker meanwhile are playing together for a record eighth time and are aiming to emulate their victory in 2009.
Kelly also won while partnering Rod Pampling ten years ago.
Charles Howell and South African Rory Sabbatini were third along with Kevin Chappell and Kevin Kisner, who are on 16 under after two rounds.
A shot back were Charley Hoffman and Billy Horschel along with Smylie Kaufman and Justin Thomas on 15 under.
Meanwhile Lexi Thompson and Bryson DeChambeau were sitting in 10th at 11 under after a second round 71.
Thompson, a seven-time winner on the LPGA Tour, is only the second woman to compete in the event following Annika Sorenstam's appearance with Fred Couples in 2006.
Thompson, who delighted the Tiburon galleries on Thursday with a brilliant eagle on the 18th, once again drew one of the biggest cheers of the day with a 16-foot birdie putt on the par-three eighth hole.