The Red Sox have used nine different relievers to start 21 games over the past two seasons.

Brennan Bernardino (9 starts), Zack Kelly (3), John Schreiber (2), Kaleb Ort (2), Joe Jacques (1), Justin Garza (1), Nick Robertson (1), Tayler Scott (1) and Chase Anderson (1) were all used as openers.

But the number of bullpen games should decrease dramatically in 2025 because chief baseball officer Craig Breslow has acquired an abundance of starting pitching depth through trades and signings dating back to last offseason. Starting depth was Boston’s No. 1 issue. It’s now potentially its top strength.

• BETTING: Check out our MA sports betting guide, where you can learn basic terminology, definitions and how to read odds for those interested in learning how to bet in Massachusetts.

Boston opens spring training camp next month with the possibility of a six-man roster that would consist of Garrett Crochet, Tanner Houck, Brayan Bello, Walker Buehler, Kutter Crawford and Lucas Giolito.

Breslow said the rotation has a chance to reach an “elite level” and there’s plenty of depth beyond those six starters.

Cooper Criswell, who started 18 games for Boston in 2024, is eligible for a rare fourth minor league option in ‘25. So he could be placed in Triple-A Worcester’s starting rotation and used as depth.

Richard Fitts, who posted a 1.74 ERA in four starts for Boston after receiving his first big league promotion in September, is likely to begin the season in Worcester’s rotation.

The WooSox’s rotation also could include Criswell, Quinn Priester, Hunter Dobbins and Michael Fulmer.

Boston signed Patrick Sandoval, the Angels’ 2024 Opening Day starter, to a two-year deal as well. He underwent Tommy John surgery last June and the Red Sox expect him to return at some point in the second half.

The Red Sox also haven’t ruled out using Josh Winckowski as a starter. He has worked to increase fastball velocity and improve his slider this offseason. He has a minor league option remaining and so he also could be placed in Worcester’s rotation.

“We’ve batted around some ideas,” Breslow said recently about the possibility of a six-man roster. “I think we’ll need to get to spring training, see how everyone reports and make a decision from there. But we’re very open to a number of solutions. I don’t think it’s possible to have too much starting pitching depth. We know we’re going to call on more than just five guys, whether that’s right out of the gates or at some point during the season.”

Breslow said Fulmer — who spent last season sidelined while he recovered from a UCL revision surgery — likely will be used as a starter. He’ll be in camp as a non-roster invitee on a minor league deal. He has made 90 big league starts and won the 2016 AL Rookie of the Year as a member of the Tigers.

“He’s a guy we actually signed with an eye on — once he’s completely healthy — building him out, whether that’s as a starting pitcher or someone who can handle bulk, leverage innings,” Breslow said at the Winter Meetings last month. “It’s something we still feel confident in. He’s making quite a bit of progress throwing pain-free and having a fairly normal offseason at this point. We’re optimistic both about his recovery and the contributions he can make just given what we saw when he was pitching as a reliever prior to him getting hurt.”

Breslow accumulated this depth through trades (Fitts, Priester, Crochet) and free agent signings (Criswell, Giolito, Buehler, Fulmer).

Priester, a former first round pick, is still just 24 and increased his fastball velocity during his two months in the Red Sox system following a deadline trade from the Pirates.

Fitts, who turned 25 last month, made significant steps throughout last season, including increasing his fastball velo, after Boston acquired him from the Yankees in the Alex Verdugo trade last offseason.

Breslow said the Red Sox don’t want pitchers bouncing back and forth between starting and relieving throughout the season like they were forced to do with Winckowski last year.

Having this amount of starter depth should help the Red Sox to establish roles early and stick to them. It should improve the bullpen as well.

Garrett Whitlock can return to being a full-time reliever, a role he thrived in during 2021. He has a 2.65 ERA in 132 ⅔ career innings out of the bullpen.

The Red Sox also have the flexibility to use young hard-throwing starters such as Dobbins (who they added to the 40-man roster) in multi-inning relief roles this season if needed.