The world number 101's three-under-par round of 67 put him on 12-under, clear of a trio tied for second comprising England's Harry Hall and fellow Americans Chris Gotterup and Kevin Roy.
"I felt like I was hitting some really good hold shots against the wind," said Riley, who has one previous win on the PGA Tour, after gusty conditions at the Waialae Country Club in Honolulu.
The 29-year-old Riley said the goal for Sunday would be to "do what I did on the back nine today".
"It's tough. There is wind. There are going to be bad shots. You got to make some gritty pars in these conditions," he said.
Defending champion Nick Taylor, who had been in a share of the lead after two rounds, slipped back to tied-fifth with a disappointing 70 that included four bogies.
"I feel like it's always very bunched here," said Canada's Taylor.
"Obviously here I've had great success over the last few years. I can fall back on that tomorrow in any scenario starting out."
The event is the PGA Tour's first of 2026, after the cancellation of The Sentry at Kapalua because of drought and water restrictions on the nearby island of Maui.
The 62-year-old former world number one Vijay Singh - having made the cut by two strokes in his first PGA Tour start since 2021 - carded a tidy 68, to sit eight strokes off the lead.