With two top-10 finishes and six top-25s this season, Watson is currently 57th in FedEx Cup points. He finished tied for 32nd in last week's U.S. Open.
Watson began his day with a bogey at No. 10 but made four birdies after that in the relatively benign morning conditions.
Windy conditions kept many of those who began their rounds in the afternoon from matching the scores of their early rising counterparts. Still, Harrington managed a 66 despite teeing off at 12:40 p.m.
"It did get windy out there," Harrington said. "It was a challenge but there were still opportunities to make birdies."
Harrington hasn't won since the 2008 PGA Championship, his third career major. The 41-year-old Irishman has missed four cuts this season but is playing relatively well lately. He finished 10th at the St. Jude Classic two weeks ago and tied for 21st at the U.S. Open last week.
Harrington, who was in contention to win here in 2010 and 2012, made birdies on four of his first seven holes Friday.
BMW INT'L OPEN: In Munich, Germany, Ernie Els shot a 3-under 69 in the second round of the BMW International Open on Friday to maintain his one-stroke lead.
The South African made six birdies, a double bogey and a bogey, leaving him at 12-under 132 halfway through the European Tour event. Els, a two-time winner of the British Open and U.S. Open, opened with a 63 Thursday.
He is followed by Matthew Baldwin of England (69) and Alexander Levy of France (68). Defending champion Danny Willett of England shot a 65 for the day's best round and is tied for fourth place with Bernd Wiesberger of Austria.