No one got closer than three shots of the lead all day. Spieth shot a 2-under 70 to hold off Justin Rose and Phil Mickelson.
Rose, the 2013 U.S. Open champion playing in the final group of the major for the first time, and Mickelson were four shots back.
No one else was closer than seven.
Spieth became the first Masters champion to lead after every round since Raymond Floyd 39 years ago, and only the fifth in the history of the tournament. And it was a bit of redemption after he played in the final group a year ago making his Augusta debut, building a two-shot lead but fading to a runner-up finish behind Bubba Watson.