LOS ANGELES, United States - Jalen Williams erupted for 40 points as the Oklahoma City Thunder held off the Indiana Pacers to score a 120-109 victory and move to within one win of clinching the NBA Finals on Monday.

An enthralling game-five battle in Oklahoma saw the Pacers climb out of an 18-point first-half hole to get within two points 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 leaves 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 40 points, six rebounds and four assists while Gilgeous-Alexander co-starred with 31 points and 10 assists, four blocks and two steals.

"My team-mates instill a lot of confidence in me to go out and be me," Williams said. "And (coach) Mark (Daigneault) has done a good job of telling me to just be myself.

"I don't got to be anything more and that's given me a lot of confidence."

Williams said Oklahoma City's experience in game one -- when they blew a 15-point fourth-quarter lead to lose -- had helped them close out victory.

"Tonight was the exact same game as game one, to be honest," Williams said. "Learning through these finals is what makes this team good and we were able to do that."

Haliburton injury woe

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 defense clamped down on the Pacers.

"He's not 100 percent, it's pretty clear," Pacers head coach Rick Carlisle said. "But I don't think he's going to miss the next game.

"We were concerned at half time and he insisted on playing... but he's not 100 percent. There's a lot of guys in the series that aren't."

Oklahoma asserted control early in the first quarter, stretching into a 29-17 lead after Cason Wallace drained his first three-pointer of the playoffs.

With Chet Holmgren leading an inspired Thunder defensive display, the Pacers offense struggled to make any impression.

At the other end, Williams and Gilgeous-Alexander began to impose themselves, combining for 29 points in the first half.

Sensing an opportunity to build a commanding lead, Oklahoma City kept the points flowing and two Gilgeous-Alexander free throws pushed the lead to 18 points before Indiana cut it to 59-45 at half time.

With Haliburton a pale imitation of his usual self, another Thunder blowout looked on the cards.

But the Pacers improved the speed of their ball movement and an eye-catching bench cameo from Haliburton's back-up T.J. McConnell suddenly turned the tide.

The Pacers outscored the Thunder 34-28 in the third quarter to trail by just eight points heading into the final frame.

A Siakam three-pointer with just over eight minutes left made it a two-point game at 95-93 as tension swept through the Thunder's Paycom Center homecourt.

But that was as close as the Pacers would get, and with Williams and Gilgeous-Alexander combining for 20 fourth-quarter points, the Thunder pulled away to power home.

AFP