Okafor's first season in the Big Easy saw him compete in a career-high 59 games. He finished the year averaging 8.2 points and 4.7 boards while playing 15.8 minutes per game. The Duke product capped off the year with his best scoring performance of the season in the form of a 30-point game on Apr. 9 versus Golden State. He'd also finish with six double-doubles. Okafor was especially strong when filling in for an injured Anthony Davis, including a 24-point, 15-rebound performance against San Antonio on Jan. 26, a 25-point, 13-rebound performance versus Indiana on Feb. 4, and a 27-point, 12-rebound performance at Houston on Jan. 29. Okafor also recorded a season-high six blocks along with 17 points and 10 rebounds against Detroit on Jan. 23. He scored his 2,000th career point on Mar. 15 against the Suns. The 278 rebounds on the year brought him 24 shy of 1,000 for his career. Okafor also shot a career-best 58.6 percent from the field, improving his career average to 53 percent. He'd also establish a peak 17.9 PER during the campaign.

Okafor split the 2017-18 season between the Philadelphia 76ers and the Brooklyn Nets. He started his third NBA season with Philly, but an upper-respiratory infection limited his October and November playing time. In addition to the illness, Okafor found himself behind Joel Embiid, Amir Johnson and others on the Philly depth chart. But then an early December deal from Philadelphia to Brooklyn helped turn Okafor's season around. While he received roughly the same amount of playing time (12.5 minutes) in both locations, Okafor found himself much more involved offensively with Brooklyn's offense. He logged more than 22 minutes in his Nets debut against Toronto on Dec. 15, posting 10 points, 4 rebounds and a block. Beginning Jan. 3 against Minnesota, Okafor saw action in each of Brooklyn's next 20 contests. He posted 15 or more points three different times during that span. Okafor's 17-point performance against the Hawks on Jan. 12 came in just over 12 minutes worth of action. The Duke product tallied a season-high 21 points against the Timberwolves on Jan. 27. He followed up that strong effort with a season-best 13 rebounds against the Knicks just three days later. Okafor also served as a defensive anchor when needed. Over the course of a 12-game span from late January to mid-February, Okafor posted at least one rejection in all but four of those contests. But then a lower leg injury and difficult flu symptoms forced Okafor to miss all but four of Brooklyn's last 24 games.

Despite season-ending surgery in March of 2016, Okafor was ready for the 2016-17 season opener. He came off the bench and delivered eight points, three rebounds and one block in just under 16 minutes for the Sixers in a home loss to the Thunder. Okafor appeared in 19 of Philly's first 20 games, with six starts, and averaged 11.2 points, 4.4 rebounds and 1.2 blocks over that span. An early-December illness then forced him to miss three straight games. The second-year player returned Dec. 11 and started eight straight games. On Dec. 29, however, he suffered a hamstring injury that forced him to miss five of Philadelphia's next six games. On Jan. 14, Okafor started at center and posted 26 points, nine rebounds, one steal and one block across 35 minutes during a 109-93 loss to the Wizards. Right knee soreness pestered Okafor for much of January, February and March. On Mar. 12, the young center dropped in 23 points (8-12 FG, 7-8 FT) while adding four rebounds, two assists, one steal and one block across 27 minutes during in a win over the Lakers. He made his last appearance of the season on Mar. 22 with six points, two rebounds and two assists during a blowout loss at OKC. Sixers management eventually decided to shut down Okafor for the rest of the season. He ended the season with 50 appearances and per-game averages of 11.8 points, 4.8 rebounds and 1.2 blocks over 22.7 minutes per contest.

Okafor was the third overall draft pick of the 2015 NBA Draft. Selected by Philadelphia, the 6-foot-10 Chicago native appeared in 53 games (48 starts) for the 76ers and averaged 30.0 minutes of run per contest. He made his NBA debut on Opening Night, Oct. 28, during a loss at Boston. Okafor posted 26 points, seven rebounds and two blocks, plus eight turnovers, in 38 minutes during the loss. The rebuilding Sixers unfortunately lost their first 18 games of the season, with the young Okafor starting at center in each contest. On Nov. 9, Okafor registered his first career double-double with 21 points, 15 rebounds and two blocks in a home loss to the Bulls. On Feb. 6, the Duke product grabbed a season-high 17 rebounds along with 22 points during another home loss to the Bulls. On Feb. 21, the rookie delivered a season-high 31 points, as well as eight rebounds, one assist, one steal and one block, during a loss at Dallas. Things turned bad in late March when the rookie center was diagnosed with a torn meniscus in his right knee. On March 22, Okafor underwent successful arthroscopic season-ending surgery to repair his right meniscus, giving him a jump on the recovery process ahead of the 2016-17 season.