Woods, who had complained about a sore back he blamed on sleeping on a soft hotel bed this week, hit the deck after hitting a fairway wood for his second shot at the par-five 13th hole during the final round of the event won by Adam Scott.
After collecting himself, the world number one got back to his feet and made his way to the point where his shot sailed over the tee box at the adjacent hole and splashed into water and he took a drop on his way to a bogey.
Woods said he felt twinges in his back on the hole before.
"It actually started the hole before, my little tee shot there started it and 13 just kind of accentuated it," he said.
The bogey at 13 cost him in a tight race in which he had been part of a four-way tie for the lead early on the back nine. Woods had another bogey at the 15th and was bending over gingerly to take his ball out of the cup.
Woods was asked later if it was a back spasm.
"Oh yeah, big time," said the 37-year-old American. "It's definitely spasming."
Woods, a five-time winner on the tour this year, still gave himself a chance to add to his total.
He birdied the 16th and 17th holes to move within one stroke of Australia's Scott, the Masters champion, and had a 26-foot putt from off the green for a possible birdie that would have forced a playoff.
"I had a chance," said Woods.
"I hit a good putt. Thought I made it," he added of the putt that died three inches from the hole. "It was a little double-breaker and I thought I poured it in."
Woods said his back had not given him any previous trouble on Sunday until the tee shot at 12.
"I was playing pretty good, and I was hanging right there and I was only one back," he said.
"I figured I was in the perfect spot and unfortunately just couldn't finish off the rest of the day."
Woods finished up with a two-under 69 that put him in a four-way tie for second at 10-under-par.
The American was not sure about his status for next week's FedExCup event, the Deutsche Bank Championship in Boston.
"That's all hypothetical. I just got off (the course) and I'm not feeling my best right now."
(Editing by Greg Stutchbury)
