Harrington was 12 shots worse than his course-record 61 in the opening round.
Dufner, trying to play more conservatively when he doesn’t feel confident about attacking, made it through another round at Innisbrook without a bogey and posted a second consecutive 5-under-par 66 to take a two-shot lead into the weekend.
“Pretty stress-free round,” Dufner said.
Harrington didn’t feel as though he hit the ball much worse in a round of 73. He realized it would be difficult to back up his record score on the Copperhead course with another low score, and it crept into his putting, especially on the back nine.
“I’m happy with my game, but when you shoot a good score, it’s hard to match the next day,” Harrington said.
William McGirt had 68 and joined Harrington at 8-under 134.
Luke Donald, who can return to No. 1 in the world with a win, had 68 and is in the large group at 7-under 135 that included Puerto Rico winner George McNeill.
EUROPEAN TOUR: In Marbella, Spain, Eduardo De La Riva, a Spaniard ranked 610th in the world, shot 3-under-par 69 to take a one-stroke lead after two rounds in the Andalucia Open.
De La Riva, who has made nine unsuccessful trips to European Tour qualifying school, is at 8-under 136 on the Aloha course. He qualified for the event though the Spanish regional money list.
Tournament host Miguel Angel Jimenez shot 68 to join Pablo Larrazabal (69), Matteo Manassero (73), Damien McGrane and Tommy Fleetwood (69) at 7- under.
Former Augusta State golfer Oliver Wilson shot 67 and is among eight players tied for seventh place, two shots off the lead.
Manassero and England’s Robert Rock are trying to play their way into the Masters by moving into the top 50 in the World Golf Ranking by March 26.
Manessero is ranked 63rd and Rock is 56th. Rock is tied for seventh after rounds of 69-69.
CHAMPIONS TOUR: In Newport Beach, Calif., Bernhard Langer birdied the final hole for 6-under-par 65 and a share of the first-round lead with Bobby Clampett and Olin Browne in the Toshiba Classic.
Langer, the 2008 winner, holed an 8-iron from 143 yards for an eagle on the par-4 sixth hole in his bogey-free round at Newport Beach Country Club.
LPGA TOUR: In Phoenix, top-ranked Yani Tseng shot 2-under-par 70 to take a one-stroke over five players after the second round of the LPGA Founders Cup.
Second-ranked Na Yeon Choi was second along with fellow South Korean players I.K. Kim and Meena Lee and Japan’s Ai Miyazato and Mika Miyazato.
Paula Creamer was two strokes back along with defending champion Karrie Webb, Karen Sjodin, Inbee Park, Jiyai Shin and Hee Young Park.