OKLAHOMA CITY — Mark Daigneault and Mitch Johnson, the two competing head coaches in the Western Conference finals, were in total alignment before the first game of the series Monday night.

To them, questions about their starting lineups were overblown, with both answering like most NBA coaches do when asked about the first five on the court.

“It’s overemphasized relative to what I’m thinking about,” Daigenault, the Oklahoma City Thunder’s coach, said. “It’s like, there’s no difference to me between who you start and who the first sub is or the next sub after that. …  If the lights went out for the first sub and they made a big deal about that, everybody would focus more on that.”

Tell it to the players.

For most, the starting lineup is a badge of honor, the first celebration of the competition to follow. The cheers and the boos preview the intensity that’s to come. It’s a lot — an emotional experience.

And it’s why teams, especially ones that are deep into the playoffs, don’t often put rookies in that position.

The San Antonio Spurs didn’t have that choice on Monday night. De’Aaron Fox was too hurt to play, so there was only one move to consider. Dylan Harper, for the first time this postseason, was going to hear his name before the tip.

He said he learned it about an hour before his team won an instant classic, a 122-115, double-overtime masterpiece. He said he prepared like it would be any other game. But it most certainly was not.

This Spurs opponent destroys teams that show any sign of indecision, any moment of weakness. They run on turnovers like a racecar runs on gasoline. They hounded and harassed Harper’s teammate, Stephon Castle, forcing him into 11 turnovers.

They push and pressure, grab and grapple, ram and rattle. Eventually, it breaks you.

But Harper handled every bit of it, cementing his place near the top of this loaded rookie class and giving the Spurs a 1-0 series lead after they stole homecourt advantage.

He turned the ball over just once — early in the first overtime — when he bobbled a pass that bounced off his leg and out of bounds. His lack of mistakes didn’t come with an ounce of passivity. A slow shooting start didn’t demoralize him. The Thunder’s defense never deterred him. He reached into his duffel bag of layups and found ways to finish at the rim by being too strong, too crafty and too poised.

He turned 20 early in March.

“Go in with the mindset of just being me,” he said.

It’s unclear when Fox will return, but if this is Plan B, it sure seems good enough.

Harper scored 24 points, as many as Shai Gilgeous-Alexander. He had six assists, more than every player on the Thunder except the MVP. He grabbed 11 rebounds, more than Chet Holmgren or Isaiah Hartenstein.

He had seven steals, more than any rookie in the playoffs since Darrell Walker had seven for the New York Knicks in 1984.

“I didn’t know Dylan could guard like this,” teammate Carter Bryant said. “To be honest, I played with Dylan a lot in high school. I’ve been playing with, against Dylan since I’ve been a sophomore in high school. So everybody has known he’s been uber talented in terms of scoring offensively. But … being able to guard a guy like Shai, being able to guard a guy like Jalen Williams and whoever and so forth defensively, it shows you how much he’s committed to winning.

“I don’t think it was a leap. I think we’re a team that really responds to challenges. And I remember early in the season, Mitch challenged him to be a very good defender, and he did it.”

Only nine rookies have scored more than 24 in a conference finals. Only one other Spur, Kawhi Leonard, started for the team in his first year in the penultimate round. Other rookies who started in the conference finals include Larry Bird, Magic Johnson, Charles Barkley and Jayson Tatum. The last one to make his first start in the West finals was Phoenix Suns reserve center Joel Kramer in 1979.

The only other rookies in NBA playoff history with 24 points, 11 rebounds and six assists are Mitch Richmond, Magic, Kareem Abdul-Jabbar and Elgin Baylor. None had seven steals (Johnson once had six). None had one or fewer turnovers.

Here’s another list: Eleven rookies played more minutes this year than Harper. Eight scored more points, and seven took more shots. Six had more assists.

“It’s just been very rewarding for someone that’s tried to support him through this year and help him in terms of coaching him at times and giving him guidance of just trusting us,” Johnson said. “’Cause he was this good eight months ago. But we wanted him to get some corporate knowledge and learn the program and the fundamentals of this league and how tough it was, and to get in better shape, and etcetera.

“And he watched a lot of guys, in terms of his rookie class, put up bigger numbers than him.”

None are still playing, while Harper is only getting better.

“Earlier in the season when everyone kind of didn’t see the vision,” Harper said, “like I kind of saw it and doubled down on it.”

Monday, that bet cashed again.