BOSTON -- Semi Ojeleye watched the film, analyzing each frame of his first NBA action and beating himself up over all the little things he might have done differently when tasked with defending some of the league's top offensive talents, including LeBron James and Giannis Antetokounmpo. Then his phone chimed.

Texts spilled in from teammate Gordon Hayward. Boston's All-Star forward, lost to a gruesome ankle injury just minutes into the 2017-18 season, wanted Ojeleye to know about how Hayward struggled his rookie season and dispensed some advice on how to guard top-level scorers.

"It says a lot about Gordon," said Ojeleye, the 37th overall pick in the 2017 draft. "He's just kinda telling me how he felt his rookie year, telling me to just trust myself and I'll be all right. Even though he's out, he's still texting me and giving me advice. Kyrie [Irving], [Aron] Baynes, Marcus Morris -- all these guys have been great. Great leaders for us young guys."

And there sure are a lot of young guys on Boston's roster.

In order to make the moves that delivered star talent such as Hayward and Irving this past summer, the Celtics had to sacrifice some of their previous depth. It also meant filling out this year's roster with unproven talent. Boston's roster currently features a staggering seven rookies among the 15 bodies available to coach Brad Stevens. Weighted by playing time, the Celtics are the third-youngest team in the league (25.0), according to Elias Sports Bureau.

Inexperienced teams are supposed to struggle. Rookies are supposed to be wildly inconsistent. But, particularly in the aftermath of Hayward's injury, the Celtics have been forced to lean heavy on those most wet behind the ears, and Boston's youngest players have routinely responded with positive results.

The Celtics are the only team in the NBA to play six rookies this season (and only one other team, the LA Clippers, has even played five, according to ESPN Stats & Info). What's more, Boston rookies have played the third-highest total of minutes (1,587) among teams this season, trailing only the Sacramento Kings (1,734) and Los Angeles Lakers (1,715) entering Thursday's action.

The Celtics have three rookies -- Jayson Tatum, Ojeleye and Daniel Theis -- who have played at least 300 minutes. The 7-17 Kings are the only other team with three such rookies, and only three other teams (the Lakers, Phoenix Suns and Charlotte Hornets) even have two such rookies, according to Stats & Info. Those four teams have combined for 34 wins and a winning percentage of .347.

The Celtics, rather improbably, are an NBA-leading 22-4.

"I love it. You want to play against the best. That's what I dreamed of as a kid. I'm like, 'Man, I hope I guard guys like LeBron.'"

Al Horford, who at 31 seems like a dinosaur to many of his young teammates, still rubs his eyes a bit when he spies Boston's record. As optimistic as he was about Boston's overall potential this season, he expected early struggles. In the aftermath of Hayward's injury, he felt like things might get real bumpy.

But 19-year-old Tatum, the player Boston shuffled down from No. 1 to No. 3 this offseason to obtain, has been maybe the best in the 2017 class through the first quarter of the season. Ojeleye and unheralded German import Theis have emerged as key rotation players off Boston's bench.

On Wednesday night, 2016 draft picks Guerschon Yabusele and Abdel Nader, both of whom were stashed by the Celtics last season, aided the shorthanded Celtics in rallying back against the Mavericks. Boston's 16-game winning streak earlier this season might never have gotten off the ground if not for the jolt that 2017 second-round pick Jabari Bird, one of the team's two-way players, provided in an emergency call-up from the G League during Boston's first win in Philadelphia.

These young Celtics are defying what's expected of rookies.

"Especially when you've got a young group, you just never know how quick guys are going to pick up things," Horford said. "But from Day 1 with this group, when you have a group of guys [that are willing to work], you get these kind of results."

Nathaniel S. Butler/NBAE via Getty Images

When the Celtics made the shocking decision to move down from the No. 1 overall pick in the 2017 draft -- giving up the glitziest of gifts from the Brooklyn Nets trade that has helped build much of the current roster -- a good portion of the team's fan base scoffed. This, they declared, might be Danny Ainge's first misstep in an otherwise unprecedented -- and successful -- rebuild.

While Philadelphia's No. 1 pick Markelle Fultz battles shoulder woes that have kept him off the court for much of his rookie campaign, Tatum is the only player on Boston's roster to start all 26 games this season. Entering Thursday's action, he had played the most minutes among any rookie.

Tatum is second on Boston's roster in minutes played, trailing only Irving, and leads the NBA in 3-point shooting, having connected on an absurd 51.9 percent of his triples this season. This after shooting 34.2 percent from distance at Duke.

Put another way: Tatum has already made more NBA 3-pointers (41) than he did in 29 games at Duke -- and on 38 less attempts.

Tatum looks like a steal so far, especially when you consider that the Lakers might deliver Boston another high lottery pick in June as compensation for Philadelphia moving up. The Lakers deliver their pick to Boston if it's between spots Nos. 2 and 5. According to ESPN's Basketball Power Index, the Lakers currently have a 30.5 percent chance of delivering that pick.

That would be another young player who could keep Boston competitive deep into the future.

The San Antonio Spurs, whom the Celtics visit Friday night (9:30 p.m. ET, ESPN) are the gold standard for sustained excellence in a league in which the only thing more difficult than getting to the top is staying there. Stevens often gushes about Spurs coach Gregg Popovich, the system they've built in San Antonio, and how corporate knowledge has aided the Spurs in building a sustained 50-plus win team.

Putting together a Spurs-like run seemed like an impossibility in the modern NBA. The Celtics, with their developing young core that also features 2016 No. 3 pick Jaylen Brown, are still stockpiled with future assets. And they might have a chance to be the closest thing to the "next Spurs."

Popovich has openly gushed about Stevens for the way he operates both on and off the court. Before Boston topped the Spurs in late October, Popovich said of Stevens, "He's going to be a great one before it's all over with, and he's already a hell of a coach."

The Spurs thrived not just because the pingpong balls delivered them the likes of Tim Duncan, but because they found gems throughout the draft. San Antonio identified players with specific skills, nurtured them, and watched them develop into impact talent on title teams.

The Celtics are doing the same. Not that they have much of a choice this season.

When Jesusemilore Talodabijesu Ojeleye showed up for his first day of kindergarten, his teacher looked at his parents and said, "So what are we going with for a name here?"

His parents landed on Semi (pronounced Shem-ee), and the name quickly stuck. Ojeleye is proud of his Nigerian heritage, and the full version of his name still adorns his official documents, such as his driver's license.

"[My name] means, 'a gift,'" Ojeleye said. "I love having that name."

And he's likewise thankful for the gifts he's been given, particularly a strength not typically possessed by rookies. Ojeleye said he started lifting weights early in his teen years but can't take credit for his eye-popping physique.

"The rest is God-given," Ojeleye said.