NORTON, Mass. -- Tiger Woods didn't have a scientific reason for going back to the shorter Scotty Cameron putter he has largely relied on for more than two decades after a brief break from it during the PGA Championship earlier this month.

"Just stubbornness," Woods said Thursday after his opening-round 3-under 68 at the Northern Trust, the first event in the three-week FedEx Cup playoffs. "I was practicing with the other one to make sure I could get some reps and get some feel, and all of a sudden -- heck with it, I'll just put [this one] in play and see how it goes. It worked."

Woods went to the other version of the Scotty Cameron putter, he said, because the longer length put less strain on his back and allowed him to practice a bit more.

The late decision to go back to the shorter version paid off in Thursday's first round.

Starting on the 10th tee at TPC Boston, Woods played the more difficult back nine in even par before getting hot on the front side. He birdied four of the first eight holes before a wayward tee shot led to a bogey at the ninth, his final hole of the day.

"When I gave myself some chances [on the front nine], I made them," said Woods, who is four shots behind early leader Harris English.

Woods rolled in a 16-footer at the long par-3 third to get into red figures. He followed that with another birdie after getting up and down from the greenside bunker at the short par-4 fourth hole. After pars at the fifth and sixth, he converted a pair of 7-footers for birdies at Nos. 7 and 8 before the hiccup at the last.

"I like the speed of these greens," he said.

His first playoff event did not come without some drama. Woods was seen putting ice-cold water bottles on his neck before his round. He said it was nothing more than to cool off some hot oils he had used to loosen things up.

"My lower back is used to it. It's accustomed to it. We do it all the time just so I can get loose," Woods said. "I decided to put some up on my neck, and it's not as tolerant as my lower back, so it gets awfully hot. It's common in pretty much every other sport and especially hockey, those guys put some pretty hot stuff on their legs, but you become accustomed to it. My lower back is pretty immune to it, but my neck is not."

Woods is entering a potentially hectic stretch that could see him play four out of the next five weeks. After the Northern Trust, he is committed to playing next week's BMW Championship at Olympia Fields just outside of Chicago. The following week is the Tour Championship, which he won two years ago.

For that one, though, "I've got to get to Atlanta first; I'm not in," Woods said.

The top 30 players on the FedEx Cup points list advance to the Tour Championship at East Lake; Woods entered this week in 49th place. After that event, there is a week off before the U.S. Open at Winged Foot, which begins Sept. 17. The major was originally scheduled for June but was pushed back because of the three-month shutdown forced by the coronavirus.

"The top 30 guys who do qualify for East Lake, they're going to play a hefty load here, whoever those 30 guys are," Woods said.

Thursday's round was a strong first step in the chase for one of those 30 spots. The 68 matched how he started at the PGA Championship two weeks ago. At TPC Harding Park, though, Woods struggled with the longer putter the rest of the week, never quite adjusting to the speed of the greens.

"Had one good day [at the PGA Championship], the first day, and then after that I didn't really putt well," said Woods, who opened with a round of 3-under or better for just the third time since the start of 2019.