GAINESVILLE, 30 Jul 2015, (AFP) - The 23-year-old Asian star also reeled off six birdies in a row to match two-time US Open champion Retief Goosen, a South African twice Ishikawa's age, atop the leaderboard with much of the field still on the course at the 7,385-yard Robert Trent Jones Golf Club.
"It was a great day for my putting," said Ishikawa after his best round of the year.
"I just putted them perfectly. I just didn't miss a putt."
The highlight was his eight-iron ace from 180 yards at the par-three fourth, his first in the US after three in Japan and another in Puerto Rico.
"Solid strike. Landed five or six yards past the flag and back to sink in," said Ishikawa. "That was kind of a special moment."
Matching the tour record of 59 was not out of the question with two par-five holes ahead of him but Ishikawa said he was so excited that parring his way to the clubhouse was a struggle.
"I was feeling like I wasn't calm," Ishikawa said. "It took about two holes to calm down. Number five was a par-five but it was difficult for me to make par."
Ishikawa, still seeking his first US title after 115 events over seven seasons, had not gone so low in a PGA event since a 62 last August in round two at Greensboro.
The 203rd-ranked Ishikawa has missed 10 cuts this year with his only top-20 finish a share of eighth in April at New Orleans.
"Still 54 holes to go," Ishikawa said. "My goal for today was three- or four-under so it's like twice (as good)."
Americans Justin Leonard and Kevin Chappell were in the clubhouse on 64 with American Steve Wheatcroft on 65 at the $6.7 million (6 million euro) event with host Tiger Woods and defending champion Justin Rose among those still on the course.
There were two holes-in-one on the day as Rickie Fowler aced the ninth from 184 yards with a seven iron. He was four adrift on 67.
Ishikawa began on the back nine with four pars before launching his birdie putt binge with an eight footer at the par-five 14th and one half that length at 15. He dropped a 23-foot birdie at the par-three 16th and sank 17-footers for birdies at 17 and 18 before making the turn and closing the run with a six footer at the first.
"It reminds me of three or four years ago," Ishikawa said. "That was my best year for putting. It was closer to that today."
At 23, Ishikawa is only three years younger than top-ranked Rory McIlroy and just a year older than Masters and US Open champion Jordan Spieth.
"I'm still young but not too young," said Ishikawa. "Competing like Rickie and Rory and Jordan some day, that's my goal. I'm not thinking about the age."
Goosen, ranked 192nd and fighting to keep his playing rights for next season, fired four birdies on both the front and back nines in a bogey-free round and did ponder the age question at 46.
"It's nice to get the youngsters giving the older guys a bit of a chance," Goosen said. "I need to play well these next few events to make sure I'm here next year and have a job."