SAN ANTONIO — Late Thursday night, when he saw more than a dozen reporters packed into a small interview room in the AT&T Center, Warriors guard Klay Thompson shook his head and muttered to himself.

“Let’s make this quick,” Thompson said, his voice barely audible.

It was quintessential Klay: A master of efficiency, he hates wasting time almost as much as air-balling three-pointers. Thompson’s need to maximize his opportunities — each possession, each jumper, each off-day — has been the driving force behind his emergence as one of the NBA’s top two-way players.

Now, three weeks after he missed eight games with a fractured right thumb, he is playing his best basketball of the season. In helping shepherd a Stephen Curry-less team to a 3-0 series lead over the Spurs in the first round of the playoffs, Thompson has averaged 25.7 points on 63.3 percent shooting from the field and 65 percent shooting from three-point range — in addition to guarding San Antonio’s best perimeter scorers.

“I just look at Klay like a machine,” Warriors head coach Steve Kerr said. “I mean, every day he comes in, gets his shots up, doesn’t say much. He just goes to work, loves what he does, zero maintenance.”

What makes Thompson special is how little energy and time he requires to accomplish the remarkable. Unlike Curry, who seemingly uses his entire body to hoist three-pointers, Thompson is a jump-shooting metronome: plant, catch, release. His form allows for no wasted motion, particularly from the waist up.

Thompson has led the NBA in points off catch-and-shoot opportunities for three seasons in a row. This is a player who once needed only 88.4 seconds of possession, 52 touches, 33 shots and 11 dribbles to score a career-high 60 points in 29 minutes against Indiana.

In addition to owning the league record for three-pointers in a quarter (nine), Thompson holds the playoff record for threes in a game (11). No one has hit more threes in his first seven years in the NBA than Thompson (1,557).

It only helps that he shares a backcourt with perhaps the best floor-spacer in league history. But with Curry limited to 51 regular-season games — his fewest since 2011-12 — by various injuries, Thompson was still a case study in efficiency.

He only narrowly missed his stated goal of making the 50-40-90 club, finishing the regular season 48.8 percent from the field, 44 percent from three-point range and 83.7 percent from the foul line. More than 56 percent of his shots didn’t involve a dribble, and less than a third of them required him to hold the ball for at least two seconds, according to NBA.com.

“When he’s in the zone, he’s impossible to stop,” said Seth Tarver, one of Thompson’s closest friends. “It doesn’t even matter what the defense does, or anyone does. If he’s just locked in, you can’t stop him.”

Thompson’s playing style mirrors his personality.

NBA fans often chuckle at his absentminded hijinks, but those close to Thompson are in awe of his ability to compartmentalize. His off-days are spent oscillating between his favorite activities. Whether walking his beloved bulldog, Rocco, playing Tarver in chess or reading about the software boom, Thompson is fully committed to whatever he is doing.

It is a trait he developed early. In elementary school, Thompson’s teachers regularly remarked to his parents that Thompson had uncanny focus for his age. At the start of the social-media age, when attention deficit disorder was becoming rampant, Thompson rarely talked in class, loved reading and thrived in competitive environments.

“He was always a very focused kid,” said Mychal Thompson, Klay’s father. “Whatever he was doing, he wanted to do his best at it.”

In the Warriors’ locker room pregame, when most of his teammates are thumbing through Instagram or Twitter on their phones, Thompson reads the newspaper. His logic is simple: Every free moment is a chance to learn.

It is that mentality that helped him become more than just a jump shooter. Long content to stand along the perimeter and hoist threes, Thompson spent the summer after his rookie season slogging through a gantlet of defensive drills.

Now, in addition to being perhaps the best three-point shooter in NBA history not named Curry, Thompson is a daunting on-ball matchup for everyone from LeBron James to Russell Westbrook. And he is far from content. In recent months, Thompson has spent his free time honing his golf game, raising money for Wine Country wildfire relief efforts and starting a foundation to help at-risk youths.

“Nowadays, with smartphones and all the electronic devices there are, it’s easy to waste your time,” Thompson said. “So, I just try to be as efficient as I can, whether it’s learning something new, reading a book or playing golf. I just try to spend my time wisely because we don’t have much of it.”

After telling himself to make it quick Thursday night, Thompson kept his postgame media session to 108 seconds. He then sauntered out of the interview room, grabbed a box of food and headed toward the team bus.

Once again, Thompson was the first player to take his seat.

Connor Letourneau is a San Francisco Chronicle staff writer. Email: cletourneau@sfchronicle.com Twitter: @Con_Chron

Series schedule

Warriors lead series 3-0

Game 1: Warriors 113, Spurs 92

Game 2: Warriors 116, Spurs 101

Game 3: Warriors 110, Spurs 97

Sunday: at S.A., 12:30 p.m. Channel: 7 Channel: 10

Tuesday: at Warriors* NBCSBA

Thursday: at S.A.* NBCSBA

Saturday: at Warriors* TNT

* If necessary, time TBD