The American duo fired a 14-under 58 in better-ball play on Thursday to head Davis Thompson and Austin Eckroat at the par-72 TPC Louisiana layout.

Thompson and Eckroat were hot on the leaders heels' after the latter's eagle on the par-5 seventh was followed by eight-straight birdies.

Two teams are tied for third at 60 - Sam Stevens and Zach Bouchou, along with Eric Cole and Hank Lebioda.

Billy Horschel, the only player to win the Zurich in both single-play and team formats, is again in the hunt after he and Tom Hoge shot a 61 to put them in a seven-way tie for fifth.

Aaron Rai and Sahith Theegala each made eagles; Rai by spinning in a 106-yard approach shot on the par-4 13th, to post a 62.

Smalley, who has never won on the PGA Tour, made a 19-foot eagle put on the par-5 second hole after sinking a 16-and-a-half footer to birdie No.1. His tee shot on No.3 landed within seven feet to set up another birdie to put his team at four-under.

The pair of 29-year-olds then combined to birdie 10 of their final 14 holes. Springer, also seeking a maiden tour triumph, accounted for the final four birdies, highlighted by his 36-foot putt on the par-3 17th.

Cam Davis and Geoff Ogilvy shot a six-under 66.

The Australians are in a monster 12-way tie for 50th which includes Shane Lowry and Brooks Koepka.

One shot behind that cluster is Australian Karl Vilips and American partner Michael Thoprbjornsen (67).

They are outside the top 40 and in danger of missing the cut unless they can make a strong push on Friday in alternate-shot play.

The format returns to better-ball on Saturday, and back to alternate shot on Sunday.

Matt Fitzpatrick, fresh off his RBC Heritage victory, teamed with younger brother Alex to shoot an eight-under 64.

Koepka, in his first season back on the PGA Tour after four years with LIV Golf, entered the week needing a good showing to earn his first exemption for a signature event, the next of which takes place next week at Trump National Doral in Miami.

Lowry carried their team early, with birdies on five of the first eight holes. Koepka finally pitched in with a 31-and-a-half-foot birdie putt on 10, but the pair did not better par the rest of the way.