Down nine points going into the period, Duncan had already done plenty, scoring 12 points in the third and hitting his first 3-pointer of the season.
So the Spurs turned up the defensive effort, holding the New Orleans Hornets to just 13 fourth-quarter points to win 92-88 Wednesday.
"We gave up a lot in the previous quarters. It was a great way to turn it up," said Duncan, who led the Spurs with 31 points.
Brent Barry hit four 3-pointers in the fourth quarter to help the Spurs rally for their fifth straight victory. He finished with 15 points. Michael Finley added 13 and Manu Ginobili scored 12 for San Antonio.
The Spurs swept their four-game series with the Hornets, who have lost two in a row and are 4-6 in their last 10. New Orleans lost at home Tuesday to the league-leading Dallas Mavericks, 105-89.
Barry keyed the fourth-quarter rally. His third 3-pointer of the fourth quarter tied the game at 77 with 6:39 left.
Finley's 3 gave San Antonio an 80-77 lead before Pargo tied it again. Finley then hit another 3 from the same sweet spot less than two minutes later to make it 84-80 San Antonio.
Paul's alley-oop pass to Tyson Chandler for a dunk brought New Orleans within one and the Hornets took an 88-87 lead with 1:42 left off of Paul's two free throws.
Finley stole the ball on a later possession and Barry sank his fourth 3 of the quarter to make it 90-88 with 17.9 seconds left.
"Obviously that last one cost us big time," said Hornets coach Byron Scott. "Brent Barry was just sitting out there wide open. He's what? Top two or three in this league in 3-point percentage, and we left him open three or four times tonight."
West's shot wouldn't fall and Paul was called for a foul with 1.2 seconds left. Jacque Vaughn sank both free throws to seal the win.
Scott said his team played "not to lose the game instead of to win it" and said he hoped his players were upset for letting the game slip away.
"This one definitely burns because it felt like this is definitely a game that we had," Chandler said. "We could have won. Every second I thought we were going to win."
Devin Brown added 11 points for New Orleans and Chandler had 10 points and 12 rebounds.
Paul said Wednesday's loss was particularly tough because of the race for the eighth spot in the Western Conference playoffs. While San Antonio already has clinched a spot, New Orleans is just a few games below the current cut.
"It's tough, especially being in the playoff hunt. We've just got to try and win the rest," Paul said.
San Antonio had the highlight play of the first half as Duncan saved the ball from going out-of-bounds in the second quarter, then sank his first 3-pointer of the season as the shot clock expired. Duncan was 0-of-8 from 3-point range this season before Wednesday's game.
"If they allowed me to, during the All-Star game I'd join the 3-point shooting contest," Duncan joked.
With 1:16 left in the second quarter Spurs coach Gregg Popovich got called for a technical foul for complaining after Duncan was called for his second foul of the night. Popovich left the court for the rest of the half, but was back after the break.
Popovich said he thought he'd been ejected.
"I saw two different referees call a technical and I quickly added that in my head. It came out two. That means you're gone," Popovich said. "If you hang around, you get fined thousands of dollars, so I walked out the tunnel."
Asked whether somebody told him he'd just gotten one technical, Popovich joked: "Yeah, but I told them I was tired."
- During the teams' last meeting in January, Popovich was ejected in the first quarter for arguing with officials after Duncan was called for a foul.
- Wednesday's game was tied six times in the first half and saw four lead changes.
- San Antonio ended up 11-of-28 (39 percent) from 3-point range while New Orleans went 8-of-13 (61.5 percent).
- Despite losing, the Hornets outshot the Spurs from the field, from 3-point range and from the foul line.