Hazeltine, Minnesota - came back towards on Saturday in a pulsating third round of the US at Hazeltine National when defending champion moved right back into contention.
Four shots clear overnight, world No 1 Woods endured a frustrating day on the greens, finishing with a 1-under-par 71 to end the day just two shots clear of Harrington and little-known Korean YE Yang, who produced a superb 69.
Irishman Harrington would have been even closer but for a bogey at the last hole, which left a sour taste in his mouth, even if his 69 moved him back up the leaderboard.
Sweden's Henrik Stenson, after a 68, and US Open champion Lucas Glover, who shot a 71, are two shots further back on 4-under-par, while South African Ernie Els (68) and Soren Kjeldsen of Norway are still within touching distance on 3-under-par.
Woods picked up two birdies and one bogey but struggled over the closing holes, although he gave himself an excellent chance of birdie at the last, only to slide his attempt just wide.
Woods is chasing his 15th career Major but his first this year and though his lead may have been halved, all 14 of his major triumphs have come when he either led, or held a share of the lead, going into the final round.
Yang, who won the Honda Classic earlier this year, will partner Woods on the final day and will be hoping that lightning strikes twice.
The Korean overtook Woods on the final day at the 2006 HSBC Championship in Shanghai to win the championship, and said that experience could help him on Sunday.
"You never know in the world of sports and the game of golf," he said. "So just try to make every shot, just focus on every shot that I have. And then tomorrow I may end up inside the top 10, top three and even win the PGA Championship. You never know."
Els birdied four straight holes from the 12th to get to 6-under at one point, only to bogey the final three holes to drop back to 3- under-par.
Five shots is a lot to make up on Woods, but the South African said it was not an impossibility.
"I've been playing good. Felt like I've been playing good all week," Els said. "The putter was okay today. I chipped in today. So a lot of good things happened.
"The finish just wasn't great, but I'm not totally out of it. Probably need something like that tomorrow and obviously got to finish it off tomorrow." (dpa)