Couples had six birdies and a bogey in posting the best score of the day and moving to 8-under 134 after 36 holes.
Three players, including first-round leader Jeff Sluman, are tied for fifth at 4-under 138.
Couples' first round 68 was marked by three consecutive bogeys on Nos. 12-14 and he started Friday tied for seventh. He opened with a birdie on the first hole and had back-to-back birdies at Nos. 5-6 and another at the ninth hole to make the turn at 4-under.
He gave a stroke back at the 12th hole but got it back at the 13th and pulled clear with a birdie at 15.
Senior's round included four birdies and bogeys at Nos. 12 and 16.