South Sudan's basketball team nearly delivered a stunning upset to a United States team of NBA superstars on Saturday before losing 101-100 in an Olympics warm-up game in London.

LeBron James, 39, the all-time NBA scoring leader, registered a game-high 25 points, including the deciding points on a driving layup with eight seconds remaining at the O2 Arena.

South Sudan, who led 58-44 at half-time, took a late lead after an 8-0 scoring run and were poised to pull off one of the greatest shocks in international basketball before James saved the day.

"The ending was good for us -- just to feel that, to feel what it's going to feel like in Paris," US coach Steve Kerr said.

"Good experience for us. Good reminder that when we play against teams, it's the biggest experience of their lives and we have to expect everyone to play like that."

J.T. Thor, who has played for the NBA's Charlotte Hornets for the past three seasons, sank a three-pointer with 20 seconds remaining to put South Sudan into a 100-99 lead.

After James made the winning shot, South Sudan had one final possession but Carlik Jones missed a jumper with six seconds remaining and Wenyen Gabriel missed on two put-back attempts before the final buzzer.

"South Sudan was amazing," Kerr said. "I did not do a great job of preparing my team. We did not focus enough on what they are capable of and that's on me.

"I think that really allowed South Sudan to gain confidence early.

"Once we turned it up in the second half, they had already knocked down a bunch of threes and were feeling really good about themselves."

It was James who sparked a 23-5 US run from late in the third quarter to early in the fourth.

"We have to continue to take a step forward," said James, a two-time Olympic champion and four-time NBA champion.

"A lot of these teams that we're playing have been practising either one month or months in advance and we have maybe two weeks together.

"So every game, every film session, we get an opportunity. We have to try to make the most of it, not taking any steps back."

Cameroon-born Joel Embiid, who became a US citizen in 2022, added 14 points and seven rebounds for the Americans.

Anthony Davis came off the bench to produce 15 points and 11 rebounds for the US squad of NBA stars.

"We're not 100 percent together, as we saw tonight," Davis said, "But it's like I said, everything is controllable."

For South Sudan, ranked 33rd in the world, Marial Shayok scored 24 points, Jones added 15 points, 11 rebounds and 11 assists and Thor had 14 points off the bench.

Shayok plays in China and briefly played alongside Embiid with Philadelphia while Jones plays for perennial Serbian power Partizan.

The Americans will face South Sudan again in the Olympics group stages on July 31 at Lille.