Last year, Nets GM Sean Marks vowed that ownership — then split between Mikhail Prokhorov and Joe Tsai — would be willing to spend when the moment called for it.

Apparently the moment called. And Tsai answered by opening his wallet and spending big.

After landing Kevin Durant, Kyrie Irving and DeAndre Jordan all during the opening hours of free agency on June 30, the Nets gave Caris LeVert a three-year, $52.5 million rookie extension Sunday. It pushed their summer spree past $400 million.

“We already know we have an ownership group that’s ready to fork out the big money when that timing is right,” Marks said last year, when Prokhorov and Tsai were virtual co-owners.

“We know with our ownership group … you’ve got owners that are committed to building this with a foundation that has some longevity and they’re committed to this, which is great.”

Last Tuesday The Post broke the news Tsai — who’d already purchased 49 percent of the Nets — had bought the rest of the team, as well as control of Barclays Center. That also put the Alibaba co-founder entirely on the hook for a hefty payroll that looks likely to rise.

LeVert’s extension kicks in for the 2020-21 season, when the Nets will be committed to $121 million in salary. And with Joe Harris an unrestricted free agent next summer and Taurean Prince a restricted one, Tsai will likely have to pay the luxury tax to keep them.

Going into this summer, the biggest free-agent deal the Nets had ever handed out was Jeremy Lin’s three-year, $36 million contract. But they’re playing in a whole different neighborhood after their recent spree, all with Tsai’s blessing.

“We want to win,” Tsai said back in May. “We want to put a team on the floor that’s a winning team.”

The contracts handed out to Durant, Irving, Jordan and now LeVert all line up to end in 2022-23. Durant and Irving will both have player options that year, giving the Nets at worst a two-year window to contend. It could reach three if Durant returns this season, and four if both he and Irving opt-in for 2022-23.

Granted, there’s risk with all of them, from Durant’s Achilles tendon to Jordan’s decline to Irving’s knee and attitude. And LeVert’s injury history is daunting.

LeVert missed essentially half of his final two collegiate campaigns (35 games), mostly due to his left foot. He’s sat about a third of his first three years in the NBA (78 games), including three months last season due to his dislocated right foot.

But LeVert was the Nets’ best player at both the beginning and end of the season, averaging a team-high 21 points in the playoffs. A healthy 2019-20 campaign would’ve put him in line for a far bigger contract than this, hitting the market at 25 in a horribly weak free-agent class.

“Caris personifies what it means to be a Brooklyn Net,” Marks said, “and we firmly believe his best basketball is in front of him.”

They not only believe it, they’re banking on it.

Just in LeVert’s draft class, Ben Simmons and Jamal Murray both got five-year max deals, and Malcolm Brogdon a four-year, $85 million pact. A healthy LeVert makes his contract a bargain. LeVert with a better jumper makes the deal a steal for a young All-Star.

It’s the first deal Tsai has signed off on as principal owner, and for the e-commerce billionaire, it’s just the cost of contention.