The Englishman's seven-under-par opening round gave him a one-stroke clubhouse lead over the morning wave of starters in Tennessee, with American Casey Wittenberg back home in six under and Ireland's Padraig Harrington third following a 65.
That left three-time major winner Harrington a shot clear of an eight-man group in the clubhouse at four under par.
Westwood, who played next week's US Open venue Pebble Beach on Sunday and Monday ahead of the second major of the year, hit the ground running. He went bogey-free with five birdies and an eagle, going out in 29 for his opening nine holes, starting from the 10th tee, with his eagle 3 coming at the par-5 16th.
Westwood added his fifth and final birdie of the round before carding pars all the way home – the only blemish was missing a short birdie putt at the ninth, his last.
England's Greg Owen had an opening one-under 69.