The Spurs took a 2-0 lead in the Western Conference finals with Game 3 on Saturday in Memphis.
Duncan opened the extra period with a layup, then made a tiebreaking putback on Parker's missed jumper before making a runner that bounced high of the back iron and rattled in for a 91-87 lead with 1:08 to play.
The Grizzlies had a chance to tie after Jerryd Bayless hit a jumper and Parker missed one of two free throws with 14.6 seconds left, but Bayless' 3-pointer from the left wing was off-target.
