SANTA CLARA >> Robert Saleh is reprising his role as the 49ers’ defensive coordinator, a league source confirmed Friday night.

Saleh returns to a vastly different unit than he left behind four years ago.

Fred Warner and Nick Bosa are the only starters still under contract from Saleh’s initial 2017-20 regime, during which he became known for his sideline enthusiasm and parlayed that successful stint into his first head-coaching job with the New York Jets.

Saleh had interviewed in recent days to fill the coaching vacancies with the Jacksonville Jaguars (Jan. 12), the Las Vegas Raiders (Jan. 14) and the Dallas Cowboys (Jan. 16).

Saleh was to interview a second time with the Jaguars until Tampa Bay Buccaneers offensive coordinator Liam Coen re-entered the Jaguars’ picture Thursday, a day after Jacksonville fired general manager Trent Baalke. On Friday, as Coen completed his deal with Jacksonville, the Raiders hired 73-year-old San Francisco native Pete Carroll, whom Saleh worked for as an entry-level defensive assistant in 2011-13. And the Cowboys’ post went to Brian Schottenheimer, their incumbent offensive coordinator.

While Saleh returns to his former post — the 49ers’ first-ever encore for an ex-defensive coordinator — coach Kyle Shanahan still has two other key vacancies to fill on his staff: offensive coordinator and special teams coordinator.

Shanahan, at his Jan. 8 press conference, prematurely announced Klay Kubiak’s promotion to the offensive coordinator role before fulfilling the league-mandated protocol of interviewing two minority candidates. Several candidates have been interviewed to replace Brian Schneider as special teams czar.

Saleh, 45, was fired five games into this season to conclude a 20-36 tenure with the Jets; they completed their 5-12 campaign under interim coach Jeff Ulbrich, a former 49ers linebacker who recently got hired as the Atlanta Falcons’ defensive coordinator.

Saleh’s return to the 49ers was telegraphed, as he was among the first candidates interviewed after Nick Sorensen was outed.