The American world number one shot seven birdies and an eagle as he moved to 16 under and overtook Patrick Reed.
Reed (69) is joined on 12 under by fellow American Kevin Kisner (65) and Argentina's Fabian Gomez (66).
Irishman Padraig Harrington (68) is eight under and Australia's US PGA champion Jason Day is three under (73), alongside Scotland's Russell Knox (72).
Northern Ireland's Graeme McDowell is one under after a 70 at the Plantation Course in Kapalua.
Masters and US Open champion Spieth, who is bogey-free after his first two rounds, said: "It is nice to have no blemishes on the card. I want to prepare and start the year with a bang, but I'm only through 36 holes. There's a long way to go."
Rickie Fowler (67) is on 10 under, while two-time Masters champion Bubba Watson (68) is a shot further back.
Jordan Spieth leads the Tournament of Champions by four shots after shooting a nine-under second-round 64 in Hawaii.