The Mavericks had an opportunity to at least send the game into overtime. But leading scorer O.J. Mayo missed the first of two free throws with 2.7 seconds to play, then deliberately missed the second.
Dallas forward Jae Crowder pulled down the rebound but missed a three-pointer as time expired.
The Sixers improved to 9-6 because they got a little bit of everything they need to win ball games. Evan Turner, who is looking more and more comfortable, finished with 22 points.
Thaddeus Young added 20 points, and Jrue Holiday finished with 18 points and seven assists, although he turned the ball over six times.
The Sixers also received solid performances from two different sources. Maalik Wayns played 13 minutes, 17 seconds, some of them when the outcome was being determined, and finished with a career-high 10 points.
And Kwame Brown finished with six points, eight rebounds - and, most important, helped out defensively against Dallas center Chris Kaman. Kaman led Dallas with 20 points but scored only seven after halftime.
The Mavs are soldiering on without Dirk Nowitzki, who is recovering from knee surgery.
The game featured the return of former Sixer Elton Brand. The team waved goodbye to Brand in the offseason when it exercised the amnesty option. That allowed the Sixers to waive Brand but still required them to pay a portion of his salary.
Brand played well in his return, finishing with a season-high 17 points and pulling down eight rebounds against his old team.
Brand said that one of the differences in the outcome was the way the Sixers ramped up their game defensively in the second half.
"I was a part of it last year when we used to do it time and again," Brand said. "They made timely plays down the stretch."
Turner credited the play of lesser Sixers for the outcome.
"We had some guys on the second squad who stepped up and answered the challenge," Turner said. "We needed them to make plays and they did. That second squad answered the challenge and that's great for the unit. It was a great team win in general."
Contact John N. Mitchell at firstname.lastname@example.org. Follow @JmitchInquirer on Twitter