Nene answered with a dunk and, after a basket by Lowry, Trevor Ariza made a layup to make it 83-75 with 2:13 remaining.
Nine of Nene's 11 points came in the final quarter.
"I thought he was huge for us in the fourth, scoring some big baskets and anchoring our defense," Wizards coach Randy Wittman said.
DeRozan made a pair of free throws with 1:57 left, but could only make one of two when he went back to the line with 1:04 remaining, leaving Toronto down 83-78.
Wall nearly lost the ball at midcourt on the next possession but kept the play alive by calling timeout. After the stoppage he streaked in to score a layup, giving the Wizards an 85-78 edge with 45 seconds left.
Back-to-back 3 pointers by Lowry cut it to 89-84 with 7 seconds to go, but Garrett Temple sealed it by making one of two at the line.
Okafor led all scorers with six points in the first, including a fast-break slam dunk in the final second that gave the Wizards a 17-16 lead.
Beal scored seven points in the second and Price had five to give the Wizards a 40-32 lead at the half.
Toronto's 32 points at the break matched its season low. The Raptors also had 32 first-half points in an 88-82 loss to Memphis on Feb. 20.
Lowry's 3-pointer with 4:14 left in the third tied it at 49-all, but Washington scored the next seven points and closed the quarter on a 14-5 run. Beal scored nine in the third as the Wizards took a 63-54 lead into the fourth
NOTES: Newly acquired Raptors G Sebastian Telfair was activated, while F Mickael Pietrus was inactive. Telfair did not play. ... Raptors F Terrence Ross returned after missing Friday's win over New York because of flu-like symptoms. ... Five of Toronto's next six games are on the road. ... The Raptors are 2-26 when trailing after three quarters. ... Actress Rachel McAdams attended the game.