Northern Ireland's Darren Clarke claimed a solo lead at the halfway stage of the Senior Open after carding 67 at the Sunningdale Old Course on Friday.
Joint overnight leader Clarke got off to a good start, making birdies at the first and third, but he came unstuck as he made three straight bogeys on six, seven and eight.
The 2011 Open champion made one more bogey midway through the back nine before charging back to the clubhouse with four birdies on the final six holes to move to 8 under for the tournament.
Clarke will become just the fourth player to win both the Open and Senior Open if he emerges victorious at Sunningdale this week.
"It would be huge," Clarke said after his second round. "But you know, we're all long enough in the tooth to know this is only two rounds and a lot of golf to be played yet.
"I would love to have this trophy sitting behind the Claret Jug. Got to go work on some iron play, my iron play wasn't there especially around the front nine today but other than that drove the ball well. Really in the mix come Sunday afternoon and would love to improve."
Germany's Bernhard Langer is one shot back alongside America's Jerry Kelly after an excellent 3-under-par 67. Four-time major champions Ernie Els, who is playing in his first Senior Open, is one shot further back.
Joint-overnight leader James Kingston had a day to forget. The South African made his only birdie of the day at the first before struggling to five bogeys.