The San Antonio Spurs gathered at their training facility last fall to watch a film showcasing their playoff defense.

It could have been titled: “I Know What You Didn’t Do Last Summer.”

They were mostly flat-footed as Russell Westbrook sped past them for layups and Kevin Durant elevated for jumpers and James Harden made the late three-pointer that ultimately swung the Western Conference finals toward the Oklahoma City Thunder.

Spurs Coach Gregg Popovich forced his players to view their Game 5 defeat in that series in its entirety, a 108-point presentation on botched defensive rotations and missed help opportunities.

“We said, ‘We’re going to focus on this and if we do, we’ll be back in the ballgame,’” Popovich recalled this week. “‘And if we don’t, go ahead and start planning your summers.’”

Looks as though the Spurs better hold off on booking that Hawaiian getaway.

A team that could be as deficient on defense as the Andorran army has fortified itself for another march on the NBA Finals thanks largely to its enhanced ability to make stops.

Tony Parker has become as adept at stifling opposing point guards with his hands and feet as he is at making them look foolish with his passes.

At 36, Tim Duncan is on pace to block more shots per game (2.7) than he has since he was 26.

Even relatively unheralded power forward Tiago Splitter has become an occasional menace, blocking Clippers counterpart Blake Griffin’s driving layup in the final seconds before halftime Thursday.

It was an ongoing theme as the Spurs held the Clippers without a basket for more than seven minutes in the third quarter of a 116-90 victory, the latest unveiling of their stylistic makeover.

“That’s what’s going to give us a chance to beat the teams that are more talented and athletic,” San Antonio shooting guard Danny Green said, “if we play good defense and are more disciplined.”

They are wildly succeeding on both fronts.

The Spurs rank third in the NBA in defensive efficiency, measured in points allowed per 100 possessions. Last season, they ranked 11th in the same category.

Their defense has helped carry them on nights when their Big Three of Duncan, Parker and Manu Ginobili has been a fraction of itself because of injuries. During one stretch before the All-Star break, San Antonio won 13 of 14 games with its mainstays playing together for only 12 minutes 29 seconds.

Duncan has been an ageless wonder, improving on last year’s averages in points, rebounds, blocks, assists, steals and field-goal percentage. He was rewarded this month with his 14th All-Star selection.

The development of young starters Green and Kawhi Leonard has also helped, with Green becoming more than a spot-up shooter and Leonard emerging as a lockdown defender in only his second professional season.

Veteran forward Stephen Jackson likened the duo to Ginobili and himself when they first joined the Spurs a decade ago.

“The way Kawhi and Danny are playing,” Jackson said, “we can play with anybody.”

The same could be said for Parker, who outscored the Clippers’ Chris Paul, 31-4, in their latest head-to-head matchup. Parker repeatedly flustered the Clippers with his deft passing touch and even scored a backdoor layup on a nice feed from Splitter.

When Parker stepped to the free-throw line in the second quarter to complete a three-point play after driving past Jamal Crawford for a layup, a smattering of Spurs fans behind the basket inside Staples Center chanted, “MVP! MVP!”

Popovich, a man not often swayed by public perception, agrees.

“He’s really matured as a player,” Popovich said of Parker. “He used to just be a scoring point guard and didn’t realize there was a whole ‘nother world out there, and now he plays a complete game on both ends of the court.”

Though the Spurs (44-13) could finish with the No. 1 seeding in the West for a third consecutive season, they have not won a championship since 2007.

Of course, their legion of doubters seems to be only shrinking.

“It’s funny, people have been saying the Spurs’ window has been closing for like six years, seven years,” said Vinny Del Negro, the Clippers coach and former San Antonio point guard. “It ain’t closing. It’s not.”

Popovich agrees there’s something different about the franchise that has won four titles since 1999, shortly after Del Negro’s final season with the team.

“Yeah,” Popovich said. “We just have guys who played better defense than Vinny did.”

ben.bolch@latimes.com

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