Indiana guard Victor Oladipo was pulling up his game socks in front of his locker last week when he glanced up at highlights of that night’s opponent. On the big-screen TV was his childhood friend, Warriors guard Quinn Cook, hitting a three-pointer over the outstretched arm of a Utah defender.

“It’s definitely going to be dope when Kevin (Durant) gets back from that rib injury,” said Oladipo, who grew up with Durant and Cook in the Maryland suburbs of Washington, D.C. “They’ve known each other for a long time, so it’s pretty cool seeing them play together on the same floor in the highest level of basketball.”

With Stephen Curry sidelined probably until at least the Western Conference semifinals by a left MCL sprain, Cook is emerging as the NBA’s most important two-way-contract player. It helps Golden State that its new starting point guard has a deep bond, on the court and off, with its best available player.

In the 15 years since they first met on a court at Seat Pleasant Rec Center in Maryland, Cook and Durant have come to view each other as brothers. Now, when directing a fast break, Cook often doesn’t need to look to know where to find Durant wide open.

“They’ve got a great connection,” Warriors head coach Steve Kerr said. “They enjoy the playing time together, and I think it shows.”

Cook was in the fourth grade when he first heard about a rail-thin high school freshman named Kevin Durant. Though Durant had won multiple national AAU championships with lifelong friend Michael Beasley and the PG Jaguars, Durant had been mostly ignored in middle school by the area’s most respected high school coaches.

A few weeks into ninth grade at his local public school, Suitland High, Durant transferred to nearby National Christian Academy after his training partner, Charlie Bell, persuaded the coach there to watch Durant work out. Around that time, PG Jaguars coach Taras “Stink” Brown — whom Durant considers his godfather — introduced Durant to Cook. Even then, as Cook played on the PG Jaguars’ under-10 team, Durant could see the elementary schooler’s will to win.

After three years playing with Oladipo at DeMatha Catholic High School in Hyattsville, Md., Cook attended Oak Hill Academy, where Durant had spent his junior season. With Durant’s advice — “Go play for a coach you trust” — in mind, Cook, then a top-25 prospect nationally, signed to play for Mike Krzyzewski at Duke.

Buried on the Blue Devils’ bench as a freshman, Cook often returned to his locker after games to find text messages from Durant: “Don’t let them see you sweat” ... “Body language is everything” .... “Be a pro.” In summer 2013, after starting 34 of 36 games as a sophomore, Cook flew to Oklahoma City to train with Durant.

Those workouts helped set the foundation for Durant’s 2013-14 NBA MVP season. Less than a year after Durant won the sport’s top individual honor, Cook helped guide Duke to a national title.

Much of the past three years, as Cook went undrafted, was waived four times, signed three 10-day contracts and dominated the G League, Durant reminded Cook that all he needed was an extended opportunity in the NBA. After being one of Atlanta’s final preseason cuts in October, Cook agreed to sign a two-way contract with Golden State.

As Cook waited to board his flight to Oakland, he chatted with Durant on FaceTime about how far they’ve come — from the PG Jaguars’ pipeline to the roster of a defending NBA champion. Over the past five months, when not in the G League, Cook has spent much of his free time hanging at Durant’s Oakland Hills mansion.

“When he passes me the ball,” Cook said, “it’s just a dream come true, for both of us.”

It comes as no surprise to Durant that, with Curry sidelined by various injuries in recent weeks, Cook has hushed anyone who doubted whether he is an NBA-caliber player. His averages the past nine games — 19.2 points, five assists and 4.4 rebounds — essentially have ensured him a place on the Warriors’ postseason roster, especially with Curry expected to miss the first round.

“I’m excited for him, but at the same time, I know it’s an opportunity for me to kind of help and give him my experiences, and for him to also help me out as well as a basketball player,” said Durant, who returned Thursday from fractured rib cartilage that sidelined him for six games. “We’re just trying to sharpen each other.”

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

Tuesday’s game

Who: Warriors (56-21) at

Oklahoma City (45-33)

When: 5 p.m.

TV/Radio: TNT/95.7