Rahm and Palmer played 30 holes Saturday in the event delayed by rain for more than seven hours Thursday, finishing off a 7-under 65 in the alternate-shot second round and shooting 64 in best-ball play in the third. Stallings and Mullinax played 27 holes, shooting 70-62.
Rahm carried the team in the third round, making eight birdies. Palmer saved bogey on the par-3 17th after both players hit into the water, and Rahm made a 15-foot birdie putt on the par-5 18th to match Stallings and Mullinax at 23-under 193.
Brandan Grace and Justin Harding were a stroke back. The South Africans played 32 holes, shooting 68-61.
The final round Sunday will be played in alternate shot.