South Africa's Ernie Els was an impressive seven-under-par 63 on Saturday to take a one-stroke lead at the Sanford International in Sioux Falls, South Dakota.
The 55-year-old teed things off with a birdie on his opening hole, then hit three in a row on Holes 5-7. The last half of his round featured additional birdies on the 10th, 12th and 15th as he went bogey-free in surging ahead of closest pursuer Retief Goosen.
"It was an important round," Els said. "I kind of didn't quite finish it off yesterday. I had it really going yesterday, but today I was really committed to get the round finished. So yeah, I had a good start, good front nine, and I felt good on the ball and on my iron shots. Listen, we've got a round to go and a lot of golf to play, but I'm in a good position."
His fellow countryman Goosen had higher highs and lower lows, and he did it on back-to-back holes. Following a bogey on the par-4 11th, Goosen rallied immediately for three-stroke eagle on the par-5 12th.
Goosen also had four birdies to get to 5 under on the day and 10 under for the tournament.
Sitting at third at nine under is Bo Van Pelt, who like Goosen shot a five-under 65 on Saturday.
"I just kind of got off to a fast start, which was nice," Van Pelt said. "I really hit it pretty good on the back nine, though I hit a couple not great wedges, like on the last six holes."
Spain's Miguel Angel Jimenez was also five under and sits alone in fourth at eight under for the tourney.
Tied in fifth four shots behind Els are Demark's Soren Kjeldsen (65) and Argentina's Angel Cabrera (69). Cabrera had posted a bogey-free, six-under 64 to take the Friday lead.
Northern Ireland's Darren Clarke (64) is alone in seventh. Americans Tag Ridings (65) and Boo Weekley (68) are tied for eight.