Duncan bounced back from his worst game ever in the Finals, and the Spurs' combination of fresh faces and old reliables dominated the NBA's winningest team before an eager crowd that hadn't seen the Finals here since 2007.
"It shouldn't be a surprise," said Spurs coach Gregg Popvich. "These are the last two teams standing. I don't think either one of them is going to get down if they have a bad night."
The Spurs were as good as fans remembered in the old days, shutting down LeBron James until they had built a huge lead late in the third quarter.
James finished with 15 points and 11 rebounds, but missed 11 of his first 13 shots against the excellent defense of Kawhi Leonard, who had 14 points and 12 rebounds.
Game 4 is Thursday here, where the Heat are 3-22 in the regular season and so far have zero wins and one really bad beating in the postseason.
"We got what we deserved," Heat coach Erik Spoelstra said. "I didn't even recognize the team that was out there tonight."
Duncan shot 3 of 13 for nine points, his worst performance ever in his 25 NBA Finals games, in the Heat's 103-84 victory Sunday. Tony Parker wasn't much better, shooting 5 of 14 and committing five turnovers, and Manu Ginobili admitted afterward the veteran trio had to play well for the Spurs to win.
They were fine, but the lesser-knowns were better.
Parker and Ginobili combined for 14 assists, but the bigger story was the guys who had never played on this stage before.
• Neal, who went undrafted after playing for LaSalle and Towson, then playing overseas for three seasons in Italy, Spain and Turkey.
• Green, who had been cut multiple times including by James' Cavaliers and now has the shot to stick.
• Leonard, the draft-night trade acquisition from San Diego State who played the NBA's four-time MVP to a stalemate.
Mike Miller made all five 3-pointers and scored 15 points for the Heat, who broke open Sunday's game and seized momentum in the series with a 33-5 run in the second half.
The Spurs seized it right back, improving to 18-7 in the finals, the best winning percentage of any team with 20 or more games.
A brief flurry by James had Miami within 15 after three quarters, but Neal, Green and Leonard combined on a 13-0 run to open the fourth, Green's 3-pointer making it 91-63.
"All of my teammates and Pop, they do a great job of encouraging me. They continue to tell me to shoot the ball. They continue to tell me whenever I'm open, to let it fly," Green said.
The NBA hadn't made its way along San Antonio's River Walk this late in the season since 2007, and fans couldn't wait to have the Spurs back. They sang and danced and clapped around the concourse and in their seats, as if their favorite rock band had returned for a concert.
And they were thrilled to see the Duncan they recognized from his first 24 finals appearances.
He got right on the board in this one, with a short jumper 20 seconds into the game.
The party played on all right, with a huge roar when Tracy McGrady, a former perennial All-Star now in his first finals appearance as a member of the Spurs' bench, checked in midway through the fourth quarter.
Storylines Spurs take 2-1 series lead
R The Spurs set a Finals record with 16 3-pointers, seven of which come from Danny Green.
• San Antonio's margin of victory is the third largest in Finals history.