Duncan, who is expected to be named the NBA's Most Valuable Player, collected 27 points, 17 rebounds, five assists and five blocks as the Spurs surprised the Lakers, 88-85, to even their best-of-seven Western Conference semifinal series at 1-1.
"It's huge for us, we really needed this one," Duncan said. "It was a semi-must win. ... We wanted to come in here and take one. We're right where we want to be."
After the Lakers whittled a 21-point deficit to 85-84 on a pair of free throws by Derek Fisher with 91 seconds remaining, Duncan passed out of a double-team to Malik Rose, who made a layup to give the Spurs a three-point cushion with 77 seconds to play.
Fisher made 1-of-2 free throws to get Los Angeles within 87-85 with 28 seconds left. Shaquille O'Neal stole the ball from Duncan and fed Kobe Bryant, who dribbled upcourt, spun into the lane and left his feet to attempt a tying shot.
But Bryant changed his mind in mid-air and appeared to try to kick the ball out to Fisher on the perimeter. With Fisher covered, Bryant passed to himself and was whistled for a double dribble with 1.3 seconds remaining.
"I lost control of the ball," Bryant said. "I tried to tip it back to Fisher and that was an obvious violation. I just lost control of the ball. ... I was trying to pass."
"We said that if it was a situation where the ball was recovered on a loose ball and we had an open floor ... to get the ball to Kobe," Lakers coach Phil Jackson explained. "We will take that opportunity."
Duncan was fouled with two-tenths of a second remaining and made 1-of-2 free throws to complete the scoring. He was 10-of-19 from the field after going just 9-of-30 in an 86-80 Game One setback Sunday.
The loss ended the Lakers' 18-game postseason winning streak against Western Conference opponents dating to the 2000 playoffs, an 18-game tear at the Staples Center dating to February 19 and a five-game head-to-head playoff streak against San Antonio.
"It's always more fun to sweep, but going through a challenge builds character," Bryant said. "You need that, you have to have that. It makes the destination that much more enjoyable when you're going through some type of struggle."
The Spurs trailed, 21-15, before closing the first quarter with a 9-0 run, taking the lead for good on a 3-pointer by Bruce Bowen with six seconds to go in the period.
San Antonio extended the advantage to 56-35 on a 3-pointer by Antonio Daniels with 29 seconds left in the first half and took a 16-point lead into the locker room.
Los Angeles closed to 59-55 on a dunk by O'Neal with 6:28 left in the third quarter before Duncan answered with a layup and free throw, helping the Spurs increase their lead to 73-65 entering the final period.
"We have to give it to San Antonio because they had a good game plan -- they came at us early," Jackson said. "We were caught in foul trouble in that first half and we could not get on any track. Their defense played well against us again. Our second-half effort was good, but they played well under our charge that we made in that third quarter."
"I think the most important part of the game for us is when they came back in the third quarter and made a good run," Spurs coach Gregg Popovich said. "When we built the lead again, I thought that was great for us to do. It showed how focused they are, and they continued to play for the 48 minutes as they have the whole year."
Duncan made it 82-69 on a hook shot with 8:48 to play before the Lakers started their late push.
Daniels scored 14 points, Bowen 13 and Rose nine and 11 rebounds for the Spurs, who shot 46 percent (34-of-74) after connecting at just 32 percent in Game One.
"I was able to be in key spots and battle for rebounds," Rose said. "These games are all going to come down to the wire -- they execute their stuff and so do we."
Bryant had 26 points and O'Neal 19 for the Lakers, who shot 45 percent (34-of-75) en route to just their second defeat in the last 22 playoff games. Plagued by foul trouble throughout, O'Neal did not speak with the media after the contest.
Game Three is Friday in San Antonio.
"We want to go home and play better than we did tonight," said Duncan, who committed half of 10 turnovers in the fourth quarter. "I've got to take care of the ball better."
"We don't have a choice now," Bryant said. "We have to improve. We have to go up to San Antonio now and play well in Game Three. I, for one, am looking forward to that. I'm sure we'll all be up for the challenge and we'll all play our best basketball."