The 37-year-old center took control in overtime for a second straight game, this time scoring the first five points as the Spurs rallied from an 18-point deficit to beat the Memphis Grizzlies 104-93 Saturday night.
That put them a win away from their first finals since 2007.
"He was huge for us the other night in overtime and got it done for us, and he did it again tonight," Spurs coach Gregg Popovich said of the two-time MVP. "That's why he is considered as great as he has for the last 17 years. He's been unbelievable. He feels a responsibility to carry us in those kinds of times, and he did it again tonight."
Duncan wants to get back to the Finals after being on the verge last year. He said he was more aggressive in overtime after being a bit tentative with his shot in regulation.
"I'm not worried about how old I am or whatever, whatever it may be," Duncan said. "I'm very focused on having another opportunity to make it to a championship and try to win, that's all."
The Spurs grabbed a 3-0 lead in the Western Conference finals and now have won five straight this postseason. With the memory of blowing a 2-0 lead a year ago in the West finals to Oklahoma City, when they lost the next four, the Spurs shook off their sloppy play early and pushed the young Grizzlies to the edge of elimination in the first West final played in Memphis.
The Grizzlies knocked off the Clippers after trailing 0-2 and upset the West's top seed in Oklahoma City in the semifinals. Now their task is even tougher with Game 4 in Memphis on Monday night.
"We've been fortunate to get this far, and we've got to play better if we want to continue," Grizzlies coach Lionel Hollins said.
Memphis set up for the final shot to win in regulation, but guard Mike Conley missed on a runner at the buzzer. He said he went a little too deep in the paint on the shot.
No NBA team has lost a series when leading 3-0.
"It is frustrating, but you know it gives us hope at the same time knowing that we can fight our way back," Conley said. "And we have had chances to win each of these games. This was a tough one to swallow, but it was a good learning lesson. There's no group of guys I'd rather be with down 3-0 to try to fight back in it."
San Antonio, which didn't lead this game until the opening minute of the fourth quarter, can wrap up the series Monday in Memphis and get back to the Finals for a shot at their fifth title as a franchise.
"One of the best wins I've witnessed being a Spur," Spurs guard Manu Ginobili said.
The Spurs hit eight of their 10 shots in overtime, with Duncan scoring seven of his 24 points. He also had 10 rebounds. Tony Parker had five of his 26 in overtime, and even Tiago Splitter, playing with four fouls, scored six in the extra five minutes to finish with 11.
"For whatever reason, we didn't panic," Parker said of a start that included four turnovers in the first quarter. "We knew they wanted to come with a lot of energy in the first half. We played our game and came back."
Mike Conley led Memphis with 20 points. Marc Gasol had 16 points and 14 rebounds, Zach Randolph added 14 and 15, and Quincy Pondexter had 15 points. But the Grizzlies, who thrived at the free throw line in knocking off Oklahoma City, got there only 18 times and made only 10.
The Grizzlies last led 85-84 with 1:04 left in regulation on a 15-footer by Gasol. After that, they managed only to tie it up twice, the last on a layup by Randolph with 4:28 left in overtime. Duncan scored and knocked down the free throw with 4:10 remaining to put the Spurs ahead to stay.
The Spurs dominated the Grizzlies in the paint, outscoring Memphis 58-42 to offset their 17 turnovers, which the Grizzlies turned into 25 points. After the Grizzlies outscored San Antonio in the first quarter, the Spurs outscored them in each of the final three periods and overtime, where they had an 18-7 edge to put away the win.
Memphis, which had a lead for only 90 seconds in San Antonio, opened up with its trademark grit and grind defense, forcing eight turnovers in the first quarter to grab an 18-point lead. The Spurs quit turning the ball over and whittled away that lead to set up a doozy of a fourth quarter where the teams swapped the lead 11 times with 10 ties -- all in the final 17 minutes.
"They went small real quick, and we couldn't contain the pick and roll ...," Gasol said. "It's painful to watch."
With neither team leading by more than two in the final 8 minutes of regulation, fans stayed on their feet, holding their "Believe Memphis" towels trying to will the Grizzlies to yet another win.
Ginobili scored seven of his 19 points in the quarter, and he put the Spurs back up first with a layup with 1:19 left and then a pair of free throws with 54.5 seconds remaining. But Ginobili also picked up his fourth foul, giving Tony Allen a chance to split free throws and tie it up at 86 for the ninth time. Ginobili then missed a 3-pointer with 20.9 seconds left with Allen getting the rebound.
With the Spurs taking control in their second straight overtime win in this series, they pushed their lead to as much as 11 down the stretch and sent fans heading toward the exits.
The Grizzlies lost for the first time at home this postseason and just their second since Feb. 8. Conley, who led the NBA in total steals this season, set the tone with a steal on the Spurs' first possession.
Parker, who set a career high in the postseason with 18 assists in Game 2, finished with seven turnovers. San Antonio turned it over eight times in the first, with the Grizzlies stealing seven of those, prompting Popovich to pull his starters and go with five fresh Spurs.
"It was one of the worst starts I've ever seen," Popovich said.
Memphis went up by as much as 18 and was ahead 29-13 at the end of the first quarter.
The Spurs opened the second quarter with an 11-2 run and hit 10 of their first 15 to pull within 42-36. The Grizzlies went into halftime up 44-40.
In the third, the Spurs pulled within a point six different times only to see the Grizzlies hit another bucket to hold onto the lead. San Antonio closed the quarter with a 12-4 run and trailed 65-64 on a bucket by Duncan.
The Spurs picked up in the fourth quarter and finally got their first lead of the game on a corner 3-pointer from Danny Green -- his first bucket of the game -- with 11:45 left to set up the back and forth quarter.
Duncan had his 144th postseason double-double, moving into second by himself behind Magic Johnson. ... Conley's five steals in the first quarter were the most in a quarter of a playoff game over the past 10 postseasons, according to Elias Sports Bureau. He finished with five turnovers. ... The Grizzlies had their 16th straight postseason sellout. ... The Spurs now have played five overtime periods this postseason, the most in franchise history. ... The Grizzlies are 1-2 in overtime games this postseason.