HOUSTON -- There was not a single pitcher in the D-backs' bullpen Sunday afternoon who opened the 2021 season there.

It's been that kind of year for Arizona, with manager Torey Lovullo forced to juggle relief roles on a regular basis as players were shuttled on and off the active roster. Because of that, the skipper is using the final weeks of the season to see which pitchers will be part of a hopefully improved ‘pen in 2022.

That's what happened in Sunday's 7-6 loss to the Astros, in which the bullpen faltered in a three-run eighth inning.

"I just wanted to get a look at some other arms, some other guys," Lovullo said. "I thought it would be a great learning environment for certain guys ... to execute and get big outs and continue in their development."

So with his team leading 6-4, Lovullo brought in Luis Frías to open the seventh inning.

Frías, 23, was called up Saturday after pitching at High-A Hillsboro, Double-A Amarillo and Triple-A Reno this season. The right-hander has a power fastball, a spike curveball, a split-changeup and, the D-backs believe, a big future.

After retiring the first batter he faced, Frías walked a pair of hitters and recorded a strikeout of Jose Altuve before walking Aledmys Díaz to load the bases.

Lovullo went to veteran Noé Ramirez to get out of the frame, but rather than push Ramirez for another inning, he brought in Brandyn Sittinger for the eighth.

"I think trying to get Frías through that seventh inning was pretty critical," Lovullo said. "We thought about one-plus [innings] with Noé, but we’ve been using him pretty good. Noé would have had the eighth, and then we would have migrated into the bullpen maybe a little differently in the ninth."

Sittinger, who pitched in independent ball for a few months in 2019, was signed by the D-backs but did not pitch during 2020. He pitched well at Double-A and Triple-A this season, earning himself his first promotion to the big leagues at age 27 on Sept. 7.

A walk to the first batter he faced got things off on the wrong foot, and when shortstop Josh Rojas bobbled a grounder and could only get one out rather than a double play, Sittinger gave up back-to-back homers to Jose Siri and Chas McCormick to give the Astros a 7-6 lead.

"I think Sittinger walked himself into some problems by walking that leadoff batter," Lovullo said. "This is a tough environment. [The Astros are] doing very well in the AL West, and they’ve got good players.

“I just felt like it was a really good opportunity for us to see some different pieces and see what they looked like, acted like and how they responded with execution. It’s part of the game. I was excited for the opportunities that those guys got."

With the loss, the D-backs finished their three-city, nine-game road trip -- which also included games with the Mariners and Dodgers -- with a 3-6 mark. 

They do, however, head back home with a little better idea of what their less-seasoned players can do. 

"We want to make sure we get these evaluations right," Lovullo said. "This is a really good experience for them and a way for us to see what is happening inside of a very tough environment."