Only one team in the history of the NBA have shot the ball better and lost, with Chicago doing it twice in the 1981 season.
Simmons copped plenty in his return to Philadelphia, just as he did on his first visit in November after a drawn-out trade request saw him exit the city as public enemy No.1.
Harden didn't play in that game, but he made up for it with 23 points and seven assists on Wednesday night.
His two three-pointers and a driving assist in the final four minutes were crucial after the Nets came from 17 points behind to level.
Simmons (12 points, five assists, five rebounds), who entered this week with more fouls committed than field goals, was scoreless with just one field goal attempt in a tepid first half.
He produced a barnstorming third quarter that yielded 10 points, including a driving floater on the buzzer to breathe life into the Nets.
Seth Curry (season-high 32 points) - another former 76ers star - then took up the slack after Simmons copped a technical foul and was benched for most of the final quarter.
Curry and Kyrie Irving (30 points) were the drivers of a 18-4 run that allowed the Nets to tie the game, before Harden steered the hosts home.
Joel Embiid had 26 points in his first clash with former teammate Simmons.
It was the 76ers' fifth-straight win while the Nets have lost five of the past seven games without Kevin Durant.
Simmons forecast even more heat from the crowd if his side, currently fourth in the eastern conference behind the second-placed 76ers, had to return for a post-season series.
"It's the coach's decision and I can't really control that," Simmons told reporters of his time on the bench down the stretch.
"I want to be out there."
In Oklahoma, Trae Young had 33 points and 11 assists to help Atlanta beat the Thunder 137-132, despite Australian second-year talent Josh Giddey's 16 points, eight rebounds, six assists and two steals.
Shai Gilgeous-Alexander scored 36 points but, down by two with 15 seconds left, had a shot blocked and then missed another attempt to seal the result.
Giannis Antetokounmpo had 33 points and 14 rebounds as the Milwaukee Bucks defeated the short-handed Denver Nuggets at home 107-99, Joe Ingles (five points, two steals, one assist) earning 27 minutes of court time.