Rain-interrupted second round saw McIlroy struggle to keep pace with the leaders while Spieth's grand slam bid looks unlikely.
PGA Championship: Matsuyama co-leads as Day surges in to contention
Hideki Matsuyama birdied five of the last seven holes to seize a share of the lead with Kevin Kisner in Friday's storm-hit second round of the 99th PGA Championship.
World No 3 Matsuyama, coming off a World Golf Championships victory last week at Akron, fired a bogey-free seven-under par 64 to match Kisner at eight-under 134 for 36 holes at Quail Hollow in the year's final major tournament.
"I don't know if the other players should be nervous or not, but this is my first experience leading a major, or tied for the lead, after 36 holes," Matsuyama said. "So being a new experience, maybe I'll be a little nervous. But on the other hand, I'm looking forward to the weekend and seeing how I do."
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A thunderstorm that halted play for nearly an hour and 45 minutes came after Matsuyama had made three consecutive birdies starting at the 12th hole, but he took advantage of wet conditions when play resumed and added birdies at the par-5 15th and par-3 17th.
"I'd have to say my putting has really saved me," Matsuyama said through a translator. "I've hit some good shots and some loose shots. Overall the putting has been the key factor.
"I've been able to read the putts the last couple weeks. I've used a new putter too. That may have helped."
Matsuyama, whose six top-10 finishes in 20 prior major starts include a runner-up effort at this year's US Open, could become the first Japanese man to win a major title and only the second Asian man to claim a major crown after South Korea's YE Yang at the 2009 PGA.
"The important thing is to give myself an opportunity to win," Matsuyama said. "Keep knocking on the door and someday it will open."
Matsuyama, who made three birdies in a row before the delay, stretched the streak to four with a tap-in birdie at 15, then sank a seven-foot birdie putt at the par-3 17th.
Australia's Jason Day, the 2015 PGA winner and last year's runner-up, fired a 66 to stand third on 136.
Sharing fourth at five-under 137 in the clubhouse were Italy's Francesco Molinari, with a bogey-free 64, and South African Louis Oosthuizen, who shot a bogey-free 67.
There are 25 players who must finish their second rounds starting at 7:30am (3.30pm UAE) on Saturday. The top contender among them is American Chris Stroud on five-under with five front-nine holes remaining.
Long after 25th-ranked Kisner reached the clubhouse with his second consecutive 67, players once fearful of lightning-fast greens attacked the dampened putting surfaces after the delay and soared up the leaderboard.
"When we got delayed, the whole course changed with regards to how receptive it was," Day said.
Day, also on a run of three consecutive birdies after a tap-in eagle at seven when the delay came, found trees off the tee and a bogey at 11 when play resumed, but bounced back with a 46-foot birdie putt at 13 and a 12-footer at 14.
"Eagling 7 and having three birdies after that was nice," Day said. "It's just unfortunate because I was actually in a rhythm and the momentum was going my way and we got called off."
Day ran between shots from the 17th green to the 18th green in the gathering gloom, trying to keep as much twilight as possible as he closed with four pars.
Kisner, seeking his first major title, sank a 48-foot eagle putt at the seventh to highlight his second round.
"I'm hitting the ball really nice and things are going my way. I'm enjoying that," Kisner said. "My bad shots are working out, my good shots are working out and I'm making putts. I'm loving playing right now."
Kisner, a US PGA Tour winner three months ago at Colonial, won his first US PGA Tour victory at Sea Island, Georgia, in 2015 in his 109th attempt.
Fourth-ranked Rory McIlroy fired his second consecutive 72 to stand 10 shots adrift. He made four bogeys in five holes on the front side, then answered with birdies at the par-5 seventh and par-4 eighth.
"Anything under 71 today is a good score," McIlroy said before the rain. "It's amazing how they have been able to make this course so much tougher."
World No 2 Jordan Spieth, who won the British Open last month, is chasing his fourth career major title and completion of a career grand slam at age 24, but closed with a bogey to shoot 73 and stand 11 strokes off the pace.
"It was more gettable after the rain delay than it was before, no doubt," Spieth said. "I played even par after the delay and that's not very good."
* Agence France-Presse