"We knew we had to come in aggressively," said Jrue Holiday, who led the guards with 17 points.
In addition to Holiday, fellow guards Evan Turner and Lou Williams had 16 and 14 points, respectively.
With the Sixers trailing by 69-64, Williams went down hard on a drive to the basket, but no foul was called on Bulls 7-footer Omer Asik, who was credited with a blocked shot.
Williams stayed in the game and afterward said he had a lower-back bruise.
"I played through a lot of pain before, and this is no different, and I will be fine," Williams said.
With the Sixers leading by one, Turner drove to the basket and drew a foul with 20.1 seconds left and expanded the margin to 77-74 by hitting both free throws.
Turner showed plenty of character on the play after getting his shot blocked by Luol Deng. He kept fighting, got the rebound, and eventually was fouled.
"I kept fighting and fighting and finally got the foul," Turner said.
The entire Sixers team showed plenty of fight after training by 14 points early in the fourth quarter.
"We were down 14, and guys decided we were going to compete today," Wiliams said.
With Chicago's Derrick Rose out for the playoffs with a knee injury, it has become apparent that the 76ers have the edge in the backcourt.
So the Sixers went after the Bulls, aggressively, early.
Of course, what hurt the Sixers was the first-half foul trouble of Holiday, who committed his third foul with 8 minutes, 2 seconds left in the second quarter and the Bulls holding a 26-23 lead.
Holiday was off for the rest of the half, but his teammates weren't.
Turner was aggressive, especially when former Sixer Kyle Korver guarded him or at least gave the appearance of playing defense.
Turner got by Korver twice to score four points, including a reverse layup off a spin move. Korver soon returned to the bench.
And then there was Williams, the Sixers' true sparkplug, who had a team-high 10 points at halftime.
What's interesting is that with Holiday on the bench for an extended period and the Sixers shooting 14 of 39 from the field, they still led, 40-39, at halftime.
Holiday, Turner, and Williams combined for 23 of the Sixers' 40 first-half points. Some of the shots were forced because the Sixers tried to capitalize on their strength.
The Sixers were outscored by 21-11 in the third quarter, shooting 4 of 21 from the field. Yet they overcame their sluggish third and now hold the edge in this series.
Contact Marc Narducci at 856-779-3225 or email@example.com, or follow @sjnard on Twitter.