In the dark: Spieth shoots 64, a shot back at Byron NelsonIRVING, Texas (AP) Jordan Spieth finished off a 6-under 64 just before dark Thursday and was within a stroke of the lead when the first round of the AT&T Byron SI Staff | May 19, 2016In the dark: Spieth shoots 64, a shot back at Byron Nelson / Published May 19, 2016SI STAFF