The leaders: After starting on the back and making the turn at even par, McGirt birdied Nos. 1-4 and 7-8 before a bogey on his final hole, the 503-yard par-4 ninth, during a back-nine 30 and Friday 66. Johnson made seven birdies against three bogeys as a solid follow-up to his opening-round 63.
Round of the day: Tim Clark birdied each of his first five holes and three more on the back for an 8-under 63. Clark's score Friday tied for the low round of the tournament, after three players - Johnson, Harman and Rory Sabbatini - matched it Thursday.
Best of the rest: Defending champion Jordan Spieth is at 7 under for the round and tournament after a 64 Friday, shaving seven shots from his even-par 71 in Round 1. Spieth made eight birdies but, like McGirt, bogeyed his final hole, the par-4 ninth. From a 20-year-old to a 47-year-old, part-timer Steve Stricker turned in a 6-under 65 and sits just three back of McGirt and Johnson at 9 under. Wagner, meanwhile, looked as if he was going to end the day tied for the lead, but bogeyed the ninth to close with a 65.
Biggest disappointment: Rory Sabbatini remains in the hunt at 9 under through two rounds but followed his Thursday 63 with a 70. He was the only player tied for 10th or better who failed to post a round in the 60s.
Storylines heading into the weekend: Will past champions reign again? Johnson is in search of his 12th career PGA Tour victory and his second at the John Deere. Spieth has the opportunity to claim his first two PGA Tour wins back-to-back at the same event. He'd be the first to do so since Boo Weekley won the Heritage at Harbour Town in 2007 and 2008. Stricker is in search of his 13th career victory, his first since 2012 and his - wait for it - fourth John Deere in the last six seasons. He went back-to-back-to-back in 2009, 2010 and 2011. Separately, McGirt finds himself tied for the lead after missing the cut in 13 of his 23 events this season, including last week at The Greenbrier. The 35-year-old has never won on Tour in 111 starts dating back to 2007. He has twice finished runner-up, doing so on both occasions at the Canadian Open in 2012 and again in 2013