Beal went down with a sprained ankle with 2:08 left in the fourth quarter. After being attended to by a trainer, Beal was carried off the court and through the tunnel by two teammates, keeping weight completely off both his legs.
Wall scored the next four points to give the Wizards an 88-87 lead, blocked Evan Turner's shot with 53 seconds left and added a jumper with 4.4 seconds left.
Wall finished with 16 points and six assists as the Wizards snapped a two-game losing streak and avoided their longest skid in the last month.
Dorell Wright scored 15 points to lead the 76ers, who have lost eight of their last nine.
Philadelphia held Washington scoreless from 7:56 left in the fourth until 2:34 remained. Between Nene's baskets, the 76ers went on an 11-0 run to take an 85-82 lead.
Martell Webster, who converted a four-point play on the Wizards' first possession of the game, also scored 16 points. Emeka Okafor had 12 points and 16 rebounds.
Beal added 14 points and Nene had 15 points and nine rebounds in his return after missing Washington's last two games due to a sore right shoulder.
Spencer Hawes had 14 points and 11 rebounds, and Evan Turner added 11 points and 10 rebounds for the 76ers. Jrue Holiday had 14 points and six assists and Thaddeus Young also scored 14 points
A.J. Price (bruised right thigh) also returned after missing Washington's last game. He scored two points on 1-of-7 shooting in 17 minutes.
For the second straight game, Royal Ivey replaced injured Nick Young (left ankle sprain) in the starting lineup and finished with four points and four rebounds in 24 minutes.