Padraig Harrington lost ground to Tiger Woods at the US PGA Championship but said he would remain focused on getting to the last nine holes on Sunday still in contention.

Defending champion Harrington shot a one-over-par 73 on Friday and will start Saturday's third round at Hazeltine National four shots behind Woods in a five-way tie for second with Ross Fisher, Lucas Glover, Brendan Jones and Vijay Singh, who will partner the leader in the last group out.

"Nine holes to go, that really has to be my focus for the next 27 holes, if I can get within a shouting distance with nine holes to go," Harrington said.

"You just don't know. Anybody can do anything over nine holes. So that would be the goal. Four shots is too many, but if I was a couple of shots, I'd certainly take that with nine holes to go.

"It's not that I'd expect to overhaul him, but anybody in that position would have a chance at doing it, especially on this golf course.

"There are some tough holes and there are some birdie holes, so there are opportunities for a player to catch up."