Padraig Harrington and six-time champion Tiger Woods set up a mouth-watering last-day duel for the WGC-Bridgestone Invitational with electrifying displays on the back nine in Saturday's third round. Overnight leader Harrington reeled off four birdies in six holes from the 12th on the way to a three-under-par 67 at Firestone Country Club, stretching his advantage to three strokes. Although the Irishman briefly faltered with a bogey at the par-five 16th where he duffed his fourth shot from a greenside bunker, he drained a 19-footer on the 17th green to finish at 10-under 200. Woods, seeking his fifth PGA Tour victory of the year on one of his favourite layouts, birdied four of the last six holes for a superb 65, matching the best score of the day. The 14-time major winner, whose approach play and putting were in sizzling order, sank a seven-foot birdie putt at the last to secure second place at seven under. South African Tim Clark, playing with Harrington in the final pairing, carded a 71 to lie five strokes off the lead in third with American Jerry Kelly (69). British Open champion Stewart Cink of the US and Masters winner Angel Cabrera of Argentina were among a group of 10 players bunched at four under. Woods, however, cast an ominous shadow over the rest of the elite field of 79, Harrington included. He has won the Bridgestone Invitational six times in just nine starts and said his game had improved since he clinched his 69th PGA Tour victory at the Buick Open on Sunday. “I've made some improvements and I'm more confident in what I'm doing,” Woods told reporters after piling up six birdies and a sole bogey in overcast, wet conditions at Firestone. “This week I hit the ball pretty good, especially today.” Woods paired with Harrington World number one Tiger Woods will play with holder Padraig Harrington and 2002 champion Rich Beem in the first two rounds of PGA Championship starting on Thursday in Chaska, Minnesota. Woods is scheduled to tee off with Irishman Harrington and fellow American Beem from the 10th hole at 0835 local time (1345 GMT) in Thursday's opening round. Angel Cabrera of Argentina has been grouped with US Open winner Lucas Glover and British Open champion Stewart Cink for the first two rounds at Hazeltine National next week.