The Rams and 49ers are ready to renew an old L.A.-San Francisco rivalry

It was once among the best rivalries in the NFL.

Through the 1970s and ’80s, the Los Angeles Rams or the San Francisco 49ers won all but two NFC West division titles.

The Rams’ return to Southern California after a 21-year absence could spark a renewal, starting tonight when they open their season at Levi’s Stadium on “Monday Night Football.”

It’s an entirely different landscape than when the Rams left for St. Louis after the 1994 season.

Two years ago, the 49ers vacated wind-swept Candlestick Park for their new stadium in the heart of the Silicon Valley.

And the Seattle Seahawks and the Arizona Cardinals — who joined the division in 2002 — have become the dominant teams.

The Rams were 7-9 in 2015 and have not had a winning season in years since 2003.

The 49ers finished 5-11 last season.

“The 49ers and the Rams are chasing the Cardinals and the Seahawks right now,” said Rams Coach Jeff Fisher, who worked as an assistant for the Rams and the 49ers in the early 1990s. “It’s a great rivalry.

“We’ll rekindle it from our fans’ standpoint, but until we get to that point, which we hope, personally, that it’s very soon, we have some work to do.”

That heavy lifting begins with a marquee Monday night game that not only relaunches the Rams — a 2 1/2-point favorite — but also marks the debut of Chip Kelly as coach of the 49ers.

The last time Kelly called plays on the West Coast, he was leading record-breaking offenses at Oregon. He spent the last two-plus seasons coaching the Philadelphia Eagles.

“Every coach has a history, there’s nothing secret anymore,” Rams defensive coordinator Gregg Williams said. “Every single game film in college, every single game film in the NFL.”

The game also will be the first time that Rams quarterback Case Keenum will start a season opener.

The Rams selected quarterback Jared Goff with the No. 1 pick in the draft. But a day after fellow rookie Carson Wentz led the Philadelphia Eagles to victory, Goff, a Northern California native and former California standout, will be inactive and on the sideline.

Last season, Keenum completed 22 of 37 passes for 231 yards against the 49ers in a 19-16 season-ending loss at Levi’s Stadium.

“It’s going to be great,” he said of starting the first game for the Rams in their new Los Angeles era. “It’s going to be a lot of fun.”

Rams running back Todd Gurley played only one series during the exhibition season, but the reigning NFL offensive rookie of the year said he would be ready for the increased workload Monday night.

“I’m not too worried about it,” said Gurley, who broke off a 71-year touchdown run in a victory over the 49ers last season. “Once the game comes, I feel like I’ll be fine.”

The Rams defense, led by Pro Bowl tackle Aaron Donald, features a new middle linebacker in Alec Ogletree. The game also marks the return of defensive end Robert Quinn, a two-time Pro Bowl selection coming off back surgery.

Quarterback Blaine Gabbert leads a 49ers offense that features running back Carlos Hyde. The defense is led by star inside linebacker NaVorro Bowman.

But most of the attention regarding the 49ers the last few weeks has centered on backup quarterback Colin Kaepernick and his decision to sit or kneel during the national anthem.

“I don’t see it as a distraction at all,” Kelly said.

It might be a reach to call a season opener a must-win situation for the Rams, but the game sets the stage for a Week 2 matchup at home against the Seahawks. Seattle Coach Pete Carroll will be returning to the Coliseum, where he restored USC to a national college football power, looking to avenge two defeats by the Rams last season.

An 0-2 start for the Rams would quell the buzz created by the NFL’s return to Los Angeles.

Fisher, who oversaw the move of the Houston Oilers to Tennessee in the 1990s, is thrilled to open the season after moving operations from St. Louis to Oxnard, to UC Irvine and, finally, to Thousand Oaks.

“It’s hard to imagine what we started doing back in March,” he said, adding, “The rest of the league, they don’t care what we’ve been going through.

“So we’ll go show them it was all worth it.”

gary.klein@latimes.com

Twitter: @LATimesklein