Tiger Woods of the US reacts to his tee shot on the 18th hole during the final round of the WGC Bridgestone Invitational event. Aaron Josefczyk / Reuters

A week that began promisingly for Tiger Woods on his long-awaited PGA Tour return ended in erratic fashion on Sunday when he signed off with a level-par 70 at the WGC-Bridgestone Invitational.

For much of the day, Woods was in disarray as he sprayed tee shots left and right at Firestone Country Club, but he reeled off three successive birdies from the 15th to give himself a late lift for next week's US PGA Championship.

"I had it in spurts this week," the former world No 1 told reporters after finishing well down the leaderboard at one-over 281. "I hit it really well, and then I'd lose it and get it back.

"Today was a good example of that. I hit it well starting out, then completely lost it there and tried to piece it back together at the end. I found my putting stroke at the end, too, which was nice."

Playing his first tournament in three months after being sidelined by leg injuries, Woods said his biggest problem at Firestone had been establishing trust in a revamped swing that was sending the ball straighter than before.

"I'm still struggling with my alignment and trusting the fact that the ball doesn't shape as much as it used to," the 35-year-old American said after recording five birdies, three bogeys and a double-bogey.

"I don't cut the ball as much, I don't draw the ball as much, the pattern is much tighter.

"It's weird when I look up the fairway or look at the flags. I'm used to seeing the ball move a lot more in my lines, so I'm still fiddling with that."

Woods, whose world ranking has slipped to 28, conceded he needed more competitive play under his belt to shake off rust but he was in an upbeat mood for the year's final major.

"Absolutely encouraged," he said of his first tournament since he completed just nine holes at the Players Championship in May.

Asked whether one more tournament would have been desirable before the PGA Championship at Atlanta Athletic Club, Woods replied: "It would be nice, but hey, I've got three days.

"I've just got to keep playing. It's just something that comes over time of just playing and getting the feel for it."

Watched by huge galleries as he set off in the final round, Woods made an encouraging start with birdies at the par-five second and par-three fifth, where he struck his tee shot to within a meter of the pin.