2015 champion Spieth finished the day at six under par, two shots clear of the pack.
Spieth told media this morning's round was one of his best rounds at Augusta National.
Tiger Woods is making his first appearance in the tournament since 2015 and sits at one over par.
Americans Matt Kuchar and Tony Finau share second place, shooting four under.
The tournament is set to be one of the closest in recent years with the lead changing multiple times throughout the morning.