San Antonio outscored Memphis 23-16 in the third period, turning a four-point halftime lead into a double-digit advantage in a 91-80 win Friday night.
Duncan led the Spurs with 20 points and 10 rebounds, and Tony Parker had 19 points.
The loss, as it has been for most of the season, could be partially traced to the Grizzlies' downfall after halftime. Memphis has been outscored in the third quarter 19 times this season, and won only one of those games.
"That was a tough third quarter," Memphis coach Marc Iavaroni said. "We were down four at the half, and they came out with a lot of energy and tried to put us away.
"We got down. We got down on ourselves, unfortunately, as well, and that's not going to help. That's only going to make it worse."
Duncan was 8-of-11 from the field and added five assists and three blocks. Parker also had five assists. Matt Bonner scored 16 points for San Antonio, missing only two of his nine shots from the field. Manu Ginobili added 13 points and six assists.
Hakim Warrick led the Grizzlies with 16 points, and Marc Gasol had 15 points and 11 rebounds. O.J. Mayo scored 12 points, but continued his shooting slump, going 6-of-14 from the field. Rudy Gay, the Grizzlies' second-leading scorer, had nine points.
"We needed our defense. We weren't making shots at a great rate," Spurs coach Gregg Popovich said. "Our defense helped us get through."
The defensive strategy was to make life difficult for Mayo and Gay. Mayo is the leading scorer among rookies at 19.9, and averaged 29 points in the previous three games against the Spurs.
"(Mayo) has had his way with us, and we didn't want him to go off in the third and fourth quarters," Popovich said. "We made the decision to try and blitz him every time and keep him out of the mix."
The Spurs already held a double-digit lead when Ginobili scored seven early points in the fourth. By the time Michael Finley hit a 3-pointer -- with an assist from Ginobili -- San Antonio had stretched the margin to 16.
The Spurs coasted home, making sure the Grizzlies did not extend them to double-overtime as they had six days earlier before San Antonio won 106-103.
"I just think we paid attention more on defense and made sure the top players didn't get off on a good rhythm, especially at the end of the game," Parker said. "Last game, they jumped on us. They had a very good first half. We just wanted to make sure we had a good start, and, from there, just play solid basketball."
Duncan helped get the Spurs going by scoring 10 of the their first 16 points, hitting his first five shots. That helped San Antonio open the game shooting 71 percent, including hitting their last eight shots in the first quarter.
The Spurs still were shooting above 60 percent midway through the second, but missed eight of their last nine shots in the half to finish at 49 percent. Duncan and Parker were a combined 10-of-13 in the half.
The Spurs' shooting slump at the end of the half allowed Memphis to cut a 10-point San Antonio lead to 44-40 at the break.
"I don't think it was much what they did. It's what we did," Gay said.
For the Grizzlies, there are signs of frustration after losing for their fourth straight and eighth in their last nine.
"They outexecuted us, outhustled us, outtoughed us," Warrick said. "We just didn't have it. They just wanted it more than us."