CHICAGO — Brad Stevens found out the hard way that even No. 1 seeds need to make adjustments in first-round playoff series. Stevens essentially went with the same lineups and rotations for the first two games against the Chicago Bulls and the Celtics were stunned both times.

With two full days off to prepare for Game 3, Stevens decided there had to be change. He removed Amir Johnson from the starting lineup, replaced him with Gerald Green, and went small. If the Celtics were going to get pounded on the boards again — and they did — they at least were going to spread the floor and be more effective offensively.

Inserting Green into the lineup and moving Al Horford to center resulted in a 104-87 win. But Stevens fully expects Chicago’s Fred Hoiberg to counter as the two former college coaches fully engage in a chess match as this series appears headed for seven games.

Adjustments are part of playoff basketball. Coaches generally stick with lineups and Stevens went with the lineup of Isaiah Thomas, Avery Bradley, Jae Crowder, Horford, and Johnson for 36 of the team’s 82 games, and it likely would have been more except for injury. But it took just two games to remove Johnson and give Green his first start in more than a year.

Green was an odd and surprising choice, but the former slam dunk champ ended up with a plus-5 in his 21 minutes and kept the Bulls’ defense honest because of his shooting ability. In order to win this series and make a long playoff run, Stevens needs to bypass conventional thinking with matchups.

Even if that means putting Horford at center.

What is ironic about that move is that Horford generally disliked playing center during his years in Atlanta. And one of the reasons he signed a four-year contract with the Celtics is to play power forward. But at center Friday, Horford enjoyed one of his best games as a Celtic with 18 points, 8 rebounds, 6 assists, and 4 steals.

Horford realizes that he will likely have to play center the rest of the series, but these types of moves are customary with playoff adjustments. Some coaches don’t want to be accused of panicking by making major rotation moves after playoff losses, but Stevens had to do something different for Game 3.

“I’m for whatever it takes for our team,’’ Horford said. “And the last game was for me to be a presence in the paint and hopefully we can keep building off of this and I’m going to start again at [center Sunday] so those are the things I’m going to be looking to do. I think we can keep building off of this.’’

Success supersedes comfort, so Stevens will have the undersized Horford playing against Robin Lopez in the paint. Lopez has won a majority of their one-on-one battles for rebounds but because of the Celtics’ floor-stretching, Lopez played a series-low 21 minutes, 19 seconds and grabbed six rebounds.

“I’ve always been comfortable playing both positions,’’ Horford said of center and power forward. “Yeah, in this situation for our team it’s best that I’m playing at the [center]. That way we keep four shooters around, mostly roll [to the basket], put pressure on the rim, and just being able to create out of this. So this is what’s best for our team right now and we’re all locked into it.’’

The Bulls may go Sunday without a true point guard considering the combination of Jerian Grant and Michael Carter-Williams combined for three assists (all by Carter-Williams) and seven turnovers. Without point guard Rajon Rondo, Hoiberg may be relegated to allowing Jimmy Butler and Dwyane Wade to handle the ball, create for themselves, and force the Celtics defense to react.

It will be another mid-series adjustment, necessary for survival. Since the Celtics had been embarrassed with two losses to the eighth seed on their home floor, the players seemed open to changes. Egos dissipate in the playoffs.

The Celtics were bruised after Game 2 but then responded with their best game in weeks by hitting 17 3-pointers and mostly controlling the game. Johnson, who played 20.1 minutes per game during the regular season, played six.

Rookie Jaylen Brown, who appeared jittery in the first two games, wasn’t part of the rotation. Terry Rozier, who didn’t play in Game 1 and didn’t play in two of the final four regular-season games, logged 23 minutes and scored 11 points.

Stevens was relegated to using all of his weapons and taking chances on other inconsistent players to respond from that 0-2 deficit.

“I think a lot of teams are like that when you look across the playoffs, a lot of teams that get down, get in a hole, play really well and focused,’’ Stevens said. “We have to play better [Sunday] than we did [Friday]. Like I said, last week was tough week [because of the Isaiah Thomas family tragedy] and it was good to see our guys feel good about themselves because I thought they certainly deserved to feel better about themselves and play a little bit better.

“[The deficit] is ultimately why we needed to do something a little bit different but [the Bulls will] adjust and we’ll have to counter back.’’

Gary Washburn can be reached at gwashburn@globe.com. Follow him on Twitter @GwashburnGlobe.