The 2006 European Tour rookie of the year leads Nicolas Colsaerts (66) on the Centenary Course at Gleneagles.
Jeev Milka Singh (67) birdied the last three holes to share third place with Miles Tunnicliff.
Colin Montgomerie opened with a 69, defending champion Paul Casey shot a 71 and Darren Clarke had a 73.
Warren won last year's Scandinavian Masters but has struggled this year, missing nine cuts in his last 11 events. Bothered by a neck problem for three months, he recently changed his swing.
'It seems to be working,' Warren said.
Colsaerts eagled the par-4 eighth hole after driving the green, 385 yards away. He also eagled the long 16th.
Thomas Levet aced his opening hole, hitting a 5-iron at the 208-yard 10th.