SAN ANTONIO — The swings in momentum in these NBA Finals have been so wild that it has been difficult to grasp just who is in control of the series. Maybe that’s because with San Antonio and Miami tied at two games apiece, neither team really is, or feels like it has, any semblance of control.
The Heat won Game 2 by 19, lost Game 3 by 36 and then cruised to a 16-point win in Game 4 on Thursday night to even things up. This series may be on a run of blowouts, but each game was close at halftime and felt like it could have gone either way until one or two factors conspired to bring on the avalanche.
“This series is being decided by this,” Heat coach Erik Spoelstra said, pinching his index finger and thumb together. “It might not be that way in the (scores), but in terms of how competitive it actually is.”
It’s a three-game series now. First team to two wins, with a pivotal Game 5 tonight in San Antonio.
“It’s a play here, a shot here or there with three minutes to go or could be a period at the end of the third period where you turn it over two or three times and the other team makes two shots,” Spurs coach Gregg Popovich said. “It’s a seven-point lead and you never recover. It’s just those little moments in the game that determine the outcome. It could be a call or a turnover. Very, very fine line.”
With that in mind, here’s a look at some of the keys and the obstacles for both teams.

• Why the Heat can win
They’ve got the best player in the world, and he’s finally playing like it: LeBron James was locked down in the first three games of the series, unable to get to the paint or knock down open jumpers that he always had. Finally in Game 4 he looked like the four-time MVP: 33 points, 11 rebounds and four assists.
— They don’t have to win on the road again: The Heat’s victory Thursday assured them that the series will end on South Beach, where Games 6 and 7 are scheduled to be played.
— Their small lineup worked like a charm: Spoelstra’s gamble to insert sharp-shooter Mike Miller into the lineup worked like a charm. Miller didn’t score a point in Game 4, but his mere presence forced Popovich to abandon his best defensive lineup that included big men Tim Duncan and Tiago Splitter prowling the paint. Game 3 rebounds: Spurs 52 (19 offensive), Heat 36. Game 4 rebounds: Heat 41, Spurs 36 (5 offensive).

• Why the Heat are in trouble
— Dwyane Wade’s health: The All-Star’s right knee has been aching throughout the postseason, and his teammates and coaches have seen it zap the energy and spring he normally has. He was brilliant in Game 4 with 32 points and six steals. But will his knee allow him to sustain that effort going forward?
— Inconsistency: The Heat haven’t won two straight games since about three weeks. For some reason, it seems to be a team that needs adversity to get it going. They’ve already fallen behind in the series twice. A third time would definitely be playing with fire.
— They’re not as intimidating: Even with their three All-Stars and a 27-game winning streak this season, the Heat are not striking fear into their opponents’ hearts anymore. The Pacers took them to seven games in the Eastern Conference finals, and the Spurs — from the veterans down to the youngsters — have not backed down. “I just think that teams are not afraid of them,” Hall of Famer Magic Johnson said.

• Why the Spurs can win
— Game 5 is in San Antonio: The Spurs have the early advantage in this best-of-three by getting the first one at home in front of their loyal fans. It’s a crucial one for them so they don’t have to go to Miami needing to win two in a row.
— They have already won in Miami: Winning Game 1 last week gives the Spurs the confidence to go to South Beach and get the job done. They played almost flawlessly in Game 1, with only four turnovers and holding James to 18 points. So they know what it takes to go in there and come out on top.
— They have had success against LeBron: Prior to Game 4’s monster line, the reigning MVP was completely flummoxed by Kawhi Leonard, Danny Green and the paint-clogging Spurs defense. In the first three games, he averaged 16.7 points and shot 39 percent. Rediscovering the LeBron antidote would bode well for the Spurs’ chances.

• Why the Spurs are in trouble
— Manu Ginobili has disappeared: Not just in the finals, but for almost the entire postseason. He is averaging 7.5 points on 34 percent shooting in the series and has played with a tentativeness and hesitancy that just hasn’t been there for most of his outstanding career. If the Spurs are going to have a chance, they have to get him going.
— Tony Parker’s health: The one player the Heat have no answer for is Parker, the shifty point guard who carved up Miami’s defense in Game 1. But he has been slowed by a strained right hamstring that he said “could tear any time now.” If it does, the Spurs are sunk.
— They’ve been sloppy: Since tying a finals record for fewest turnovers in Game 1, the Spurs have given it up 47 times. Miami’s defense certainly deserves a lot of credit, but the precision and cohesion that have been hallmarks of San Antonio’s offense for years were nowhere to be found in Game 4. All the mistakes allowed the Heat to get out in transition, and they turned 19 turnovers into 23 points.