Just as the Spurs must contend with LeBron James, the Heat have their own defensive challenge when the Finals begin tonight at American Airlines Arena. Spurs point guard Tony Parker, despite a bruised calf suffered in the second round, has returned to the midseason form that made him an MVP candidate for the second straight season. The 12-year veteran is coming off one of the best playoff performances of his career, a 37-point outing that sealed the Spurs’ sweep of Memphis in the Western Conference finals. Just as that conquest delivered the Spurs back to the Finals for the first time in six years, it culminated a long, often-difficult journey for Parker from his development as a 19-year-old rookie to the poised, polished floor general who will dictate his team’s fate against the Heat. “Every time he stepped on the court (in the playoffs), he was the best player,” Miami coach Erik Spoelstra said. “They have obviously Hall of Famers and a well-oiled system. But he creates so much offense for them. What you have to respect more than anything is his engine and he’s tireless to work for those opportunities.” Heat wing Shane Battier went a step further, calling Parker the third-best player in the NBA, presumably behind James and Oklahoma City’s Kevin Durant. The last time Battier faced Parker in the playoffs, he and the Memphis Grizzlies were bouncing the Spurs from the first round of the 2011 playoffs. Parker slept-walked through the first three games of that series. He eventually picked it up, but the Spurs never recovered from a 2-1 deficit. Spurs coach Gregg Popovich said Parker took that disappointment, as well as the one that followed against Oklahoma City in last year’s Western Conference finals, to heart. Combined with the leadership role he assumed for the French national team, Parker’s maturation from sidekick to focal point was complete. “With a little bit of maturity and understanding how difficult it is, he really committed himself to being mentally ready to play night after night after night,” Popovich said. “I just wanted him to be consistent, to be a leader every night. To want to get back to this stage more than he’s even wanted to in the past.” Matching his mental growth, Parker’s skill set has expanded considerably. Opponents once used to dare Parker to shoot, an invitation he wasn’t always able to take advantage of. Now he ranks among the better mid-range shooters in the game, hitting 45 percent of his attempts between 10 and 23 feet. His biggest improvement has come as a playmaker. An undersized shooting guard for most of his career, Parker now assists on 40.4 percent of his teammates’ baskets — the highest rate of his career — while averaging just 13 turnovers per 100 possessions. “I think he’s a lot better player,” Tim Duncan said when asked to assess Parker in comparison to the Spurs’ last trip to the 2007 Finals, when he was the series MVP. “He has a lot more responsibility for making our team go than he did then. And I think he’s a lot more prepared to do that. So as good as he was then, I think he’s even better now.” Which sets up perhaps the most important matchup of the entire series: Parker vs. Miami’s top-rated pick-and-roll defense. Miami point guard Mario Chalmers said Wednesday that the Heat have five basic pick-and-roll coverages, with multiple variations of each. Parker, with his speed, quickness and almost unmatched ability to use screens to his advantage, will test them all. Making matters even tougher for the Heat are the Spurs’ stable of floor-spreading shooters, a feature that helped sealed their downfall against Dallas in the 2011 Finals.