AKRON, OHIO >> Jason Day's plan for the Bridgestone Invitational was to get in the lead as quickly as possible and expand it from there.
He took care of the first part Friday.
With just enough breeze to make the fairways at Firestone seem even tighter, Day relied on his sharp short game and a pair of late birdies for a 1-under 69 that gave him a one-shot lead over David Lingmerth going into the weekend.
What irritated the world's No. 1 player was the way he finished.
Day had a 20-foot birdie putt from the fringe on the final hole, and when his putter bumped up against the collar on the way back, he rapped it too hard and then missed the 6-foot par putt on the way back.
"I was very cross with myself when I was walking off," Day said. "The great thing is that once I do silly things like that on 18, I soon forget about it, and I just need to start focusing on tomorrow's round.
"But I know that I'm putting good because I'm holing putts. And if I can give myself the opportunities, I'm hoping that I can stretch that lead over 54 holes, and then hopefully by 72 holes, I can stretch that lead even more."
Day was at 4-under 136, matching Tiger Woods in 2005 for the highest 36-hole score to lead this World Golf Championship.
Lingmerth had a 67 that tied for the low score of the second round, where scoring was hampered by wind that felt as though it were coming out of different directions. He also made bogey on the 18th, and the Swede wasn't alone in dropping shots toward the end of his round.
William McGirt, who began the second round with a three-shot lead, stayed in front until he went over the par-5 16th with a wedge and made bogey, and then chopped up the 18th hole on his way to a double bogey for a 74. McGirt had a 74 and was two shots back at 138, along with Emiliano Grillo (71) and Scott Piercy (69).
"Trying to figure out the wind was impossible," McGirt said. "It was a lot of down off the left with a touch of in off the right. I mean, who knows?"
Only nine players remained under par.
Justin Thomas hit a tee shot that caught the slope perfectly on the par-5 16th and didn't stop rolling until it was 414 yards away. He hit 5-iron just left off the green in a nasty lie and figured he had squandered a good scoring chance until his chip hit the pin and dropped for an eagle, the first one on the 16th since 2008.
"I can't hit another drive that hard," Thomas said.
He had a 69 and joined Jordan Spieth (71), Adam Scott (68) and Kevin Kisner (70) at 1-under 139.
Spieth is trying to pick up the pace, aware of criticism that he is playing too slow. Having spoken with his coach, he thinks it gives him an edge to step up and hit it.
"The quicker part actually helps me because then I just get up there and fire away," he said. "The more I can do that, actually I think the better off — kind of gun slinging mentality, just to go up and hit the way I always have played."
His only issue was keeping it in play, though he wasn't alone in those struggles.
U.S. Open champion Dustin Johnson hit only six fairways in his round of 73 that put him at 2-over 142, though he's still only six shots behind.
Everyone is chasing Day, who is trying to join Woods and Phil Mickelson as the only players to win at least two World Golf Championships in the same year. Day won the Dell Match Play in March in dominant fashion, while his victories this year at the Arnold Palmer Invitational and The Players Championship were a little closer.
It didn't feel like his best golf on Friday, though the conditions had something to do with that.
"I think over the next two days it's going to be very difficult for everyone," Day said. "I would love to be able to give myself more opportunities, and if I can do that, hopefully I'm holding the trophy at the end of the week. The mentality won't change with regards to how tight it is. I've just got to try and get it done. Even if I don't have my best stuff, just find a way to get it done."
He at least posed with one trophy on Friday, even though it will never be his.
The Cleveland Cavaliers had the gold NBA championship trophy on display at various spots around Firestone, and Day couldn't resist a photo with wife, Ellie, and the trophy.
"And LeBron James didn't come and tackle us, so that was a neat thing," he said.
His wife suffered a mild concussion late last year when they had courtside seats and James crashed into her going after a loose ball.