His teammate Joel Embiid scored 38 points and grabbed 12 rebounds, while point guard De'Anthony Melton, 24, posted a personal best in his young career, with 33 points plus seven steals.
And Harden scored nine of his 28 points in overtime to lead the Sixers to victory.
Philadelphia took a 102-84 lead early in the fourth quarter before the Lakers, boosted by 31 points and 12 rebounds from Anthony Davis, erased a nine-point deficit in the final 29 seconds to push the Sixers in overtime.
During this one, the Lakers missed their first nine shots and logically let the victory slip away.
"We should never have found ourselves in this position in the first place," Embiid said.
"That's what we've been talking about throughout this season."
"We have to be better. It wasn't good enough. We have to be focused for 48 minutes. That end (of the 4th quarter) wasn't us. But I'm glad we responded in overtime and that we ended up winning", underlined the native of Yaoundé.
Milwaukee dominates Dallas
LeBron James, who missed his first six shots, had 23 points for the Lakers.
Fullback Austin Reaves, 24, added 25 points in 41 minutes on the court.
And Russell Westbrook had the Lakers' first triple-double off the bench since Magic Johnson in 1996 with 12 points, 11 rebounds and 11 assists.
The Los Angeles franchise, only 13th in the Western Conference (at 10-15), will have to sign a series of victories if it wants to hope to hang the play-offs.
Current NBA leading scorer, Slovenian Luka Doncic scored 33 points for Dallas, but Brook Lopez scored a decisive layup seven seconds from the end to allow Milwaukee to beat the Mavericks (106-105).
Giannis Antetokounmpo of the Milwaukee Bucks during an NBA game against the Sacramento Kings in Milwaukee on December 7, 2022 © Stacy Revere / GETTY IMAGES NORTH AMERICA/AFP
Bucks star Giannis Antetokounmpo of Greece settled for 28 points, ending his eight-game streak at 30 or more.
But Milwaukee (19-6) solidified its second place in the Eastern Conference behind Boston (21-5).
Zion Williamson scored 35 points in the success of the New Orleans Pelicans in front of Phoenix (128-117), who thus maintain their lead in the Western Conference with a record of 17 wins for eight defeats.
The Suns, third, are them at 16-10.
Nets victorious in Atlanta
Williamson pulled off a spectacular dunk in the final seconds of the encounter that sparked a post-match brawl, during which several players had to be subdued.
Second in the Western Conference with one more loss than the Pelicans, Memphis kept up the pace by unsurprisingly beating Detroit, last in the East (114-103) at home.
Kevin Durant scored 34 points and Kyrie Irving added 33 points and 11 rebounds in Brooklyn's 120-116 win at Atlanta.
Harrison Barnes scored 20 points and Domantas Sabonis added 18 points and 18 rebounds to lead Sacramento to a convincing victory at Cleveland (106-95).
D'Angelo Russell's 30 points allowed Minnesota to win on the floor of the Utah Jazz (118-108).
German winger Franz Wagner scored 34 decisive points in Orlando's victory over Toronto (113-109).
Selected for the All-Star Game in 2021, Julius Randle, author of 33 points, largely contributed to New York's success against Charlotte (121-102).
Buddy Hield (c.), Indiana Pacers during an NBA game against the Washington Wizards in Indianapolis, December 9, 2022 © ANDY LYONS / GETTY IMAGES NORTH AMERICA/AFP
Finally, Bahamian Buddy Hield's 28 points helped Indiana beat Washington (121-111), despite Kristpas Porzingis' 29 points.
© 2022 AFP