The San Antonio Spurs are coming off an epic performance and look to claim a 3-1 lead in the NBA Finals when they visit the Miami Heat on Thursday. San Antonio set an NBA Finals record by shooting 75.8 percent from the field in the first half and led by as many as 25 points while rolling to a 111-92 victory in Tuesday's Game 3. Spurs forward Kawhi Leonard broke out of his funk by scoring a career-best 29 points.Miami forward LeBron James had 22 points but 14 of them came in the first quarter before Leonard clamped down on him on the defensive end. Leonard scored 16 points on 5-of-5 shooting in the opening period as San Antonio scored 41 points and had 71 at the half against the shell-shocked Heat. " One thing about (the Spurs), if you make a mistake, they're going to make you pay," James said afterward. "And they made us pay more often than not." Game 4 is doubly important to the Heat with the NBA switching from a 2-3-2 series format to a 2-2-1-1-1 as a second straight Spurs victory in Miami would put San Antonio in position to clinch the series at home in Sunday's Game 5.TV: 9 p.m. ET, ABC ABOUT THE SPURS: Leonard was a huge disappointment while averaging just nine points and two rebounds over the first two games before erupting for the best performance of his three-year career. He made 10-of-13 field-goal attempts and also frustrated James over the final three quarters. Leonard set the tone for the Spurs with the strong first quarter showing as he cast aside the tentativeness he displayed over the first two games. "I just was in attack mode," Leonard told reporters afterward. "Trying to be aggressive early. Just knocking down a couple of shots got me going. My teammates found me. They did a good job of getting me involved."ABOUT THE HEAT: Starting point guard Mario Chalmers has been a complete non-factor in the series and missed all five of his field-goal attempts while scoring just two points in Game 3. Chalmers is averaging just 3.3 points on 3-of-12 shooting and has the same number of turnovers as assists (nine apiece) as Miami is getting badly outplayed at the point-guard position. " Still at the drawing board," Chalmers said after Game 3 in response to questions about his poor play. "Everybody else is doing their job, and it's me that's not helping the team right now. And I don't want to be that guy. I don't know what it is right now but I have to figure it out."BUZZER BEATERS 1. Miami committed 20 turnovers in Game 3 - James made seven of the miscues - while G Danny Green had five of San Antonio's 12 steals.2. San Antonio shot 59.1 percent from the field in its two victories with an average winning margin of 17 points.3. The Heat have won 13 consecutive playoff games following a loss.PREDICTION: Heat 100, Spurs 97