James led the USA with 25 points and seven assists and also added six rebounds as Team USA avoided a major upset.
His Los Angeles Lakers teammate Anthony Davis added 15 points and 11 rebounds, and Joel Embiid of the Philadelphia 76ers finished with 14 points on 5-of-6 shooting and chipped in seven boards.
In its fourth of five pre-Olympics tune-ups, the USA trailed 58-44 at half-time but outscored South Sudan 37-18 in the third quarter to lead 81-76 going into the fourth quarter.
Marial Shayok and Carlik Jones carried South Sudan. Shayok, who appeared in four games for the Philadelphia 76ers in the 2019-20 season, led all scorers with 24 points. Jones, who played in 12 games over the 2021-22 and 2022-23 seasons for the Dallas Mavericks, Denver Nuggets and Chicago Bulls, amassed 15 points, 11 rebounds, 11 assists and two steals.
Jones missed a runner with under four seconds left during Sudan's final possession.
"I'm going to be honest: I like those better than the blowouts," James said after Team USA improved to 4-0 in the tune-ups. "At least we get tested."
JT Thor, who played for the Charlotte Hornets last season, scored 14 points, and Wenyen Gabriel (Memphis Grizzlies) had 11 points, six rebounds and three assists for South Sudan.
Anthony Edwards and Stephen Curry added 11 and 10 points, respectively, for the US Edwards was just 4-for-11 from the floor and Curry made 3 of 10.
The Americans were favoured by 43.5 points before receiving a battle from South Sudan.
"I did not do a great job preparing our team," Team USA coach Steve Kerr said. "We did not focus enough on what they're capable of, and that's on me.
"I think that really allowed South Sudan to gain confidence early... They were great. They played a wonderful game and the ending was good for us, just to feel that, to feel what it's going to be like in Paris and Lille."
Team USA will face Germany on Monday in London in their last exhibition game before the Paris Olympics. The first group stage game is against Serbia at Lille, France, on July 28th.
Team USA and South Sudan meet again on July 31st in group play.
