Glover, defending champion Zach Johnson and rookie Patrick Reed all finished 36 holes at the TPC Deere Run course at 12-under 130.
Reed fired a 63 early in the day, Johnson shot a 66 and Glover turned in a 62 that gave him a chance to win for only the second time since he became the surprise titleholder at the 2009 U.S. Open.
Chez Reavie turned in the day's low score of 61 and that put him at 133 in a group with three-time John Deere winner Steve Stricker.
Of the 153 players who took part in the second round Friday, 96 turned in a sub-par score. It took a 4-under 138 total to survive the 36-hole cut and among those missing it were former British Open champion Louis Oosthuizen and Jonas Blixt, who won last week's stop on the PGA Tour.
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