The surging Chicago Bears have equaled their win total of last season with three victories in their past four games.

So, aside from the usual problems they have faced on the road this season, the 49ers face a stiff challenge entering Sunday’s game at Soldier Field against a team that has made dramatic improvements from a year ago on both sides of the ball.

The two central figures on John Fox’s coaching staff are offensive coordinator Adam Gase and defensive coordinator Vic Fangio. For a short period of time in January, it appeared as if those two men would be running the show for the 49ers this season.

Fangio had complete autonomy as the chief of defense on Jim Harbaugh’s staff. The 49ers never ranked outside of the NFL’s best-five defenses with Fangio calling the shots. Last season, the 49ers were fifth in the NFL, surrendering just 321.4 yards per game. Although the 49ers have experienced a lot of turnover, Fangio certainly has a good read on the team's roster.

“Well, obviously that’s taken into account," 49ers coach Jim Tomsula said on Monday. "I’m not going to get into any game planning, but yes, I know that, we know that -- very aware of that.”

Fangio interviewed for the 49ers’ head-coaching opening after the team’s “mutual parting” with Harbaugh. However, general manager Trent Baalke, CEO Jed York and president Paraag Marathe determined then-defensive line coach Tomsula was the 49ers’ top in-house candidate.

After interviewing at least nine candidates, the 49ers narrowed the list to Tomsula and Gase, who spent the previous three seasons as the Denver Broncos’ offensive coordinator.

On Jan. 13, the eve of the 49ers hiring the man who would become Harbaugh’s successor, most of the signs pointed toward Gase getting the job.

Baalke, who was in charge of hiring the 49ers’ next coach, spent 8 ½ hours with Gase in the Denver area for a follow-up interview. Then, Baalke had an hours-long dinner with Broncos quarterback Peyton Manning, who gave Gase a resounding recommendation, according to sources.

Gase’s plan was to handle the offense and turn over the defense to Fangio, whom he felt he could convince to remain on the 49ers’ staff. Multiple sources later said that Fangio, indeed, would have remained with the 49ers on Gase’s staff.

Baalke floated the idea of Tomsula taking over as defensive coordinator, a source said. While Gase wanted to retain Tomsula as defensive line coach with a title promotion, a source said, he did not want to turn the defense over to a coach who had no experience working in the secondary. Sources said Baalke never stressed to Gase during the interview process that if Tomsula was not defensive coordinator it would be a deal-breaker.

Gase received a midnight phone call from York after spending the better part of the day with Baalke. Although neither Baalke nor York made any job offer or any promises, Gase had every reason to feel good about his chances of becoming the 49ers’ next head coach, according to sources.

Gase got a return phone call the next morning from Baalke, who informed him the 49ers had decided to hire Tomsula.

“The job was offered to one person and one person only, and that was Jim Tomsula," Baalke said two days after Tomsula was hired.

It’s not known exactly why the 49ers passed on Gase, though some have cited the possibility the team thought Gase needed more experience. Gase, who turned 37 in March, spent two seasons as a scouting assistant with the Detroit Lions before Steve Mariucci hired him to his staff as an offensive assistant in 2003.

But even after the 49ers spurned Gase for the head-coaching job, the organization put on a full-court press in an attempt to hire him as offensive coordinator, sources said.

Tomsula even traveled to Denver and met Gase at the airport, sources told CSNBayArea.com.

Gase was at the airport to fly to Chicago, where he would meet with Fox, whom the Bears had hired a few days earlier. Gase turned down the 49ers’ offer and decided to re-connect with Fox, for whom Gase worked four seasons while with the Broncos.

The teams appear to be going in different directions as they prepare to meet on Sunday.

The 49ers, who finished 8-8 in Harbaugh’s final season, have lost eight of their first 11 games. The 49ers experienced the expected offseason free-agent departures, as well as mostly unexpected losses of such players as defensive standouts Patrick Willis, Justin Smith and Chris Borland, as well as right tackle Anthony Davis, to retirements. In addition, Aldon Smith was released after his August run-in with the law.

The defense, the driving force behind the 49ers’ three consecutive trips to the NFC Championship game from 2011 to ’13, has fallen to toward the bottom of the NFL. The 49ers rank 29th in total yards allowed under defensive coordinator Eric Mangini.

Meanwhile, the Bears (5-6) have experienced a bump with Fangio. The Bears’ defense, which ranked 30th in the league before Fangio’s arrival, is now 14th.

The 49ers’ offense under Geep Chryst ranks last in the NFL in yards per game and scoring. They have scored more than 20 points just twice. Quarterback Colin Kaepernick struggled through the first eight games and was benched. He may have played his final game with the 49ers after undergoing season-ending surgery on his non-throwing shoulder.

Gase’s absence has been felt in Denver, where the Broncos’ offensive production has fallen off by more than a touchdown per game.

Gase has also pushed the right buttons with Bears quarterback Jay Cutler, who has thrown 14 touchdowns and just six interceptions. In Cutler’s nine previous NFL seasons, his best passer rating was 89.2 in 2013. He currently stands at 92.5, which ranks 10th among quarterbacks with at least 300 attempts.

Fangio and Gase, coming off the Bears' upset victory over the Green Bay Packers at Lambeau Field last Thursday, had three extra days to prepare to face the team if appeared for a while in January that they would be coaching.



