San Antonio made an NBA Finals-record 75.8 per cent of their shots in the first half to set up a 111-92 victory over Miami on Tuesday and take a 2-1 series lead.
The Spurs made 19 of their first 21 shots and finished 25 of 33 in the first half, bettering the 75 percent shooting by Orlando against the Los Angeles Lakers in 2009.
"I don't think we'll ever shoot 76 percent in a half ever again," Spurs coach Gregg Popovich said.
Unlike Game 1, when they pulled away in the final minutes, the Spurs were up comfortably before half-time in this one.
Returning to the arena where they were so close to winning a fifth championship last year, the Spurs came out playing like they were trying to build a lead that was impossible to blow.
They shot 13 of 15 and led 41-25 lead after the first quarter, then hit their first six shots of the second in front of a stunned crowd in Miami to go ahead 55-30.
Kawhi Leonard scored a career-high 29 points, sinking 10 of 13. Leonard scored only 18 points in the first two games, looking frustrated while getting into foul trouble trying to defend LeBron James in Game 2. But he had his outside shot working early and the effect on the Spurs' offense was obvious.
Danny Green and Tony Parker each had 15 points for the Spurs.
James and Dwyane Wade had 22 points each for the Heat, who host Game 4 on Thursday.
Chris Bosh scored just four points and scored nine points for the Heat, who for the second straight year will have to overcome a 2-1 finals deficit after being blown out in Game 3.
This rout came on their home floor, where they had been 8-0 this post-season and had won a franchise-record 11 in a row since the Spurs beat them in Game 1 of last year's finals.
San Antonio inserted Boris Diaw into the lineup, countering Miami's small line-up and creating more ball movement. The game got off to a crisp start, with the Spurs making their first five shots and Miami opening 4 for 4.
James had 14 of their first 20 points, but even he could not keep up with the Spurs' pace.
Miami coach Erik Spoelstra said San Antonio "came out at a different gear than what we were playing at, and it just seemed we were on our heels the most part of the first half."
Miami cut it 14 late in the first half, but the Spurs closed with a 9-2 burst to make it 71-50.
The Heat finally got into it in the third, running off 10 straight points to cut a 17-point deficit to 81-74 on a drive by Norris Cole, who had replaced an ineffective Mario Chalmers.
That was as close as Miami would get, as the Spurs pulled away in the fourth.