Jason Day fired an impressive seven-under 65 to edge two shots clear at the halfway point of the Arnold Palmer Invitational.
The Australian world number three backed up his opening 66, moving into 13 under at the Bay Hill Club and Lodge in Orlando, Florida.
Day produced a bogey-free round to sit two shots clear of Swede Henrik Stenson, who carded a 66 on Friday.
The PGA Championship winner felt he had made a perfect start to the PGA Tour event.
"It's great to be there. I'm so happy to be there, but the average is 13 or 14 under that kind of wins around here so definitely way above average," Day said.
"I just had it going on a string the last two days, putted great, hit the ball good.
"Overall, I'm very happy with how everything panned out."
Day holed three birdies on his first nine holes before four more followed in an impressive round that has him in control.
Stenson's only blemish came at the par-three second, but his fine round was enough to see him ahead of Justin Rose (66).
Like Day, Rose went through bogey-free to be well-placed heading into the weekend.
A group of four Americans sit tied for fourth and five shots off the lead, including Jamie Lovemark (68), Troy Merritt (69), Kevin Chappell (68) and Derek Fathauer (66).
Paul Casey (69), Marc Leishman (70) and Brendan Steele (70) are a further shot back.
World number two Rory McIlroy improved after starting with a 75, a five-under 67 seeing him sit tied for 42nd.