Australia’s Jason Day sank a 35-foot putt on the last to complete a superb second round and take control at the Arnold Palmer Invitational at Bay Hill.
Day, the overnight leader by one, shot 65 to move to 13 under par, five ahead of the pack midway through day two.
Northern Ireland’s Rory McIlroy shot a 67 after his opening 75, but remains 11 strokes behind Day on two under.
Jamie Lovemark led the chasers on eight under, while England’s Paul Casey is in contention after a 69 for seven under.
McIlroy has not given up hope of challenging Day over the weekend, saying: “I need to set myself a target and try to get to that, try to emulate what he has done over the first two days.
“If I was to go out and shoot a couple of 66s over the weekend I don’t feel like I would be too far away. I can’t think about Jason being 11 shots ahead of me,
“I have to make as many birdies as I can and even if that’s not good enough at the end of the week, I can take a lot of positives and a lot of confidence from that going forward.”
Day made seven birdies and no bogeys as he improved on his opening round of 66 by one stroke.
“It would be nice to go eight under tomorrow,” joked the world number three. “I said after yesterday’s round I was just trying to stay patient and came out and started off really solid and kept it up.”