Steve Nash added 24 points and 10 assists to help the Suns move within four games of idle Dallas for the eighth and final playoff spot in the Western Conference. The loss ended the 76ers' winning streak at four games.
"We're still alive," Nash said. "We still feel we can do it."
Grant Hill added 21 points for the Suns, giving them four 20-point scorers for the second consecutive game. It's the first time in Suns history the feat has been accomplished and the first time in the league since the New Orleans Hornets did it April 14 and 16, 2007.
"That was a good win," Phoenix coach Alvin Gentry said. "We're still trying to chase teams to see if we can get into the playoffs."
Richardson helped the Suns break open a close game with 11 points in the fourth quarter. O'Neal dominated the game inside, hitting 12 of 18 shots, and Nash directed the Suns' potent offense.
The first half produced a series of runs and ended with the 76ers leading 66-63, but it was marred by an injury to Leandro Barbosa, one of the Suns' leading scorers.
Barbosa, averaging 14.5 points, was forced out with 26.3 seconds remaining in the first period when he hyperextended his left knee on a drive to the basket. His status was listed as day-to-day and he will undergo an MRI on Thursday.
Richardson said that Gentry told him at halftime he needed to be more aggressive in the second half because of Barbosa's absence.
"I struggled in the first half," Richardson said. "It was rough. In the second half, Coach wanted me to step up. That's exactly what I did. "All the guys are stepping up now. We have to win almost every game now [to make the playoffs]."
Phoenix and Dallas each has 14 games left. They meet one more time, April 5 at Dallas.
The 76ers bemoaned their lack of defense.
"We tried different defenses, zones, pick and roll defenses, and it just seemed like they were scoring every time," Philadelphia coach Tony DiLeo said. "We just couldn't stop them."
"We just never got them out of rhythm," Iguodala said. "They just kept scoring and all their guys had it going, it seemed."
The 76ers had the first big run of the opening half, spurting for 10 straight points, including four each by Young and Green, taking a 23-16 lead midway through the first quarter. Phoenix rallied to grab a 29-28 lead on a layup by Lou Amundson late in the period, but Williams scored Philadelphia's final eight points of the quarter and the 76ers led 34-31.
Phoenix opened the second quarter with a 14-1 spree, capped by a 3-pointer by Matt Barnes, while holding Philadelphia without a field goal for the first 3:42.
The Suns then opened an 11-point lead, 51-40, before the 76ers started raining 3-pointers, including three straight, one by Miller and two by Donyell Marshall, wiping out the Suns' advantage.
Philadelphia, one of the league's worst shooting teams, shot 61 percent (25-for-41) in the first half. Young led the way with 14 points and Miller had 13. Nash had 16 and Hill 13 for the Suns, who hit 54.2 percent (26-for-48).
The third quarter was close throughout, with nine ties and three lead changes. Neither team led by more than five points, with the Suns holding a 93-91 edge going into the fourth period.
Richardson, with 14 points, keyed the Suns' offense during the period.
For the second season in a row, the Suns will play an outdoor exhibition game, this time against Golden State on Oct. 10 at Indian Wells, Calif. ... The 37-year-old O'Neal is averaging a career high in field goal percentage and nearly that in free throw percentage; the last player over 35 to have career highs in both categories was Robert Parish in 1980-81. ... The Suns' average of nearly 120 points per game since the All-Star break is the best in the NBA, nearly seven points better than any other team.