Joey Sindelar shot the best round of the day at the US Senior Open in Ohio to claim a one-shot halfway lead.
The American had five birdies and one dropped shot in his round of 66 to make it to five under and earn a place in the final pairing for Saturday's third round.
Sindelar birdied his first hole, the 10th, and made further birdies at the 17th and second before his only blemish came with a bogey at the fifth.
But the 58-year-old bounced back straight away with successive birdies at the sixth and seventh and parred his way home to make sure of setting the pace.
His playing partner on Saturday will be compatriot Billy Mayfair, who improved his position with a round of 67 that included four birdies and just one dropped shot.
Gene Sauers is in third on his own on three under after a round of 69, while Stephen Ames made ground into a tie for fourth with a 68.
The Canadian is joined on two under by Glen Day and the leading European challenger Miguel Angel Jimenez, whose second-round 70 included a pair of birdies and two bogeys.
First-round leader Vijay Singh dropped six shots off the pace after a rollercoaster round of 75.
Singh opened his day with a birdie at the 10th but he had three bogeys and a double on his front-nine and dropped three more strokes on the way home.
He sits on one over alongside Welshman Ian Woosnam, who shot 72 on Friday, while leading European contenders Bernhard Langer, Paul Broadhurst and Colin Montgomerie are eight shots back on three over.