US trio Chris Kirk, Philip Knowles and Andrew Putnam grabbed a share of the halfway lead at the Rocket Classic.
After five straight missed cuts, Knowles eagled three of the four par fives at Detroit Golf Club en route to a 64 as he moved to 14-under par, Kirk joining him after a second 65 which started with three birdies.
Putnam's 66 in the less favourable conditions later in the day completed the leading trio, one ahead of fellow American Jackson Suber who included five successive birdies in his round of 65.
Meanwhile, despite improving on his opening-round 73, Seamus Power finished on level par for the tournament with golfers at six-under and better making it through to Saturday and Sunday.
Joint overnight leader Aldrich Potgieter is among a trio on 12-under-par after a 70 on a day when he lost his share of the course record - set with Kevin Roy in the first round.
Jake Knapp went one better with an 11-under-par 61 and a blemish-free round which included an eagle and nine birdies.
That left him in a large group on 11-under-par which also includes England’s Harry Hall and David Skinns, Roy and major champions Hideki Matsuyama and Collin Morikawa, who credited a change of putter for his 64.
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