An enthralling game-five battle in Oklahoma saw the Pacers climb out of an 18-point first-half hole to get within two of the Thunder in the fourth quarter.
But just as Indiana threatened the latest in a series of trademark comebacks, the Thunder found an extra gear with Williams and NBA Most Valuable Player Shai Gilgeous-Alexander steering the team to a pivotal victory.
The win put the Thunder 3-2 up in the best-of-seven series, meaning they can seal the NBA crown with victory in game six in Indianapolis on Thursday.
Williams finished with a career playoff high of 40 points, along with six rebounds and four assists, while Gilgeous-Alexander co-starred with 31 points, 10 assists, four blocks and two steals.
Pascal Siakam led the Indiana charge with 28 points but the Pacers were left sweating on the health of star point guard Tyrese Haliburton after the loss.
Haliburton, whose fitness has been under a cloud since game two of the series, left the game in the first quarter with a right calf problem before returning later in the contest.
The Pacers talisman finished with just four points from a bitterly disappointing outing – all of them coming from free throws – as the Thunder’s vaunted defence clamped down on the Pacers. (AFP)