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 to shoot 1-under 69, taking a one-shot lead over David Lingmerth.
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.
"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 67 to tie for the low score of the second round, where scoring was hampered by wind that seemed to be coming out of different directions.
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 74. McGirt 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.
He had 69 and joined Jordan Spieth (71), Adam Scott (68) and Kevin Kisner (70) at 1-under 139.
U.S. Open champion Dustin Johnson hit only six fairways in his round of 73 that put him at 2-over 142, six shots behind.
PGA: Greg Chalmers birdied five of his last eight holes to take a two-point lead in the Barracuda Championship at Reno, Nev., a modified Stableford scoring event. The 42-year-old Australian had a 10-point round to reach 24 points in the system that awards eight points for double eagle, five for an eagle, two for a birdie and deducts one point for a bogey and three for a double bogey or worse. First-round leader Martin Laird and Gary Woodland are tied for second.
LPGA: Defending champion Brooke Henderson and Suzann Pettersen shared the lead at 11-under 133 after the second round of the Cambia Portland Classic. Pettersen shot the day's low score, 8-under 64, and Henderson shot 68 at Columbia Edgewater. Mariajo Uribe shot 67 and is one back.