He came home in just 31 shots, six under par.
"If I do what I did today each day, we're in good business", added Spieth, who had seven birdies in his bogey-free round. After winning five tournaments in 2015, including his first two majors, Spieth is extending the success he had in 2015.
Day was unlucky on the last when his makeable birdie putt lipped out of the hole on the left side and he had to settle for par. Jordan Spieth is a slight favorite (+470) over Jason Day (+520) with Dustin Johnson (+765), defending champion Patrick Reed (+930) and Bubba Watson (+975) not far behind.
Spieth birdied the last on the way to a seven-under 66 to stand alone in second, with Brandt Snedeker, J.B. Holmes and Danny Lee on 67.
Van Zyl maintained the form that put him in ties for eighth and 13th at the season-opening Alfred Dunhill Championship and Nedbank Golf Challenge before Christmas, hitting six birdies and an eagle. "Whatever it is, we want to keep it going".
"Any time it's mentioned that it's a new year, it's nearly as if the questions that are asked are, 'How in the world are you going to do what you did last season?' Well, I should get a little better each time I go and practice, right?" he said.
Making his debut in the event on the Plantation Course in Kapalua, Knox fired a two-under-par 71 to sit tied for 19th in the 32-man field made up of winners from the United States circuit in 2015.
Jim Furyk wanted nothing more than to be in Kapalua, Hawaii, for the start of the new year on the PGA Tour.
"Maybe we want to beat each other so bad it brings the best out in us", Spieth said.
Reed wasn't converting many chances, with two-putt birdies on the par 5s on the front. He then proceeded to end his round with a 16-foot eagle putt at the 18th. He followed with a pitch to tap-in range on the 14th and 15th holes, and a shot over the gorge to 2 feet on the 17th. He arrived last Wednesday and spent four days playing the Plantation Course before the tournament week began. He was ready to go, and when it counted, he looked sharp. Because this tournament consists of previous year winners only, we can get value in the middle of the pack for those who have seen the course before. They're hard to read.