Washington shot 35 percent from the field in first quarter and finished at 40 percent overall.
The Wizards battled back in the second half, pulling within six with 8:37 left.
"One half we were ready to play and the second half we got real lackadaisical," Jackson said. "We started clock watching instead of playing defense and they were able to get back into the game and that wasn't acceptable if you all had heard Pop coming in here and screaming."
Wall had 15 points in the second half, Webster added 10 and Nene and Chris Singleton each scored all 11 of their points in the final two quarters.
Jackson refused to blame Duncan's injury for the lack of focus in the second half, but it clearly had an impact.
"That's going on through everybody's mind — 'What's happening?'" he said. "To have our best player go down like that holding his knee and ankle is kind of frustrating but we had a game to play. We don't know how long he's going to be out, but we've still got to get the job done regardless of who is out there."
Splitter re-energized the Spurs, scoring on a dunk and a reverse layup to make it 77-67 with 7:28 left. Splitter had six points and two rebounds in the final quarter and Parker added five points and three assists.
"In the second half, we lost our focus and the defense dissipated and that let them get back in the game," Popovich said. "Once again, Tony and Tiago were great. They were steady the entire night. We got it done."
NOTES: Spurs G Manu Ginobili was sidelined by left hamstring tightness. ... Washington F Trevor Booker (sore left wrist) was a late scratch. ... The Wizards have had nine different leading scorers for an individual game, with six in the last 10 games. ... Washington's last win in San Antonio was 99-89 on Dec. 11, 1999. ... Wall was averaging 13.7 points, 6.5 assists and 2.9 rebounds since returning from injury. ... San Antonio was playing its final home game before its annual "Rodeo Road Trip." The Spurs will play nine straight road games while the San Antonio Livestock Show and Rodeo is held at the AT&T Center.