Michael Kim and Andrew Putnam hit the front after the second round at the Zurich Classic of New Orleans, where former world number one Jordan Spieth and 2017 Masters champion Sergio Garcia were notable casualties.
American duo Kim and Putnam took a one-stroke lead following their three-under-par 69 as the PGA Tour tournament switched to alternate shot Friday following Thursday's four-ball format.
The alternate format saw one player hit the tee shots on the even-numbered holes and the other on odd numbers, and the Kim-Putnam partnership was almost flawless with five birdies and just the double-bogey at the fifth hole to be 13 under through 36 holes.
Last year's runners-up Kevin Kisner and Scott Brown ended the second round within striking distance of their countryman at TPC Louisiana.
Kisner and Brown carded a two-under-par 70 heading into the weekend.
Two-time Masters champion Bubba Watson and Matt Kuchar excelled in the alternate shot format.
Watson and Kuchar moved up the leaderboard courtesy of a five-under-par 67 to be nine under and three strokes behind Kim and Putnam.
It was a forgettable day for Spieth and fellow competitor Garcia as the star golfers departed the event.
Spieth and team-mate Ryan Palmer (74) missed the cut by one shot after finishing with consecutive double-bogeys – the former finding the water on both occasions.
Sergio Garcia and fellow Spaniard Rafa Cabrera Bello (73) followed Justin Thomas and Bud Cauley (70) out of the tournament, while overnight leaders Zhang Xinjun and Dou Zecheng (80) sensationally capitulated.