CINCINNATI -- Reds starting pitcher Justin Dunn seemingly had everything going in his favor against the Cardinals on Tuesday night. But with Dunn's history, manager David Bell and pitching coach Derek Johnson took zero chances when his right shoulder felt tight.

Dunn was pulled after four innings, but the bullpen picked him up with five scoreless innings as Cincinnati cruised to a 5-1 victory over St. Louis at Great American Ball Park.

"His stuff was just a little bit down the last inning. We just wanted to be safe right there," Bell said of Dunn. "Fortunately, our bullpen came in and was just outstanding. As far as Justin's concerned, he's been pitching really well. We just want to make sure we keep him going in the right direction with his injuries. I'm very confident he'll be back to make his next start."

Dunn, who was acquired from the Mariners in the March trade for Jesse Winker and Eugenio Suárez, missed the last two-thirds of the 2021 season with right shoulder inflammation. After a long rehab process, he is 1-2 with a 4.63 ERA in five starts since joining the Reds' rotation Aug. 8.

In his four innings vs. the Cardinals, Dunn gave up one run on three hits with no walks and four strikeouts. He struck out three of his first four batters on the night and has a 2.40 ERA over his past three starts.

"He just continues to get better out there," catcher Austin Romine said. "Continues to own the command of his pitches, all of his offspeed pitches and his fastball. He was pitching really well and being aggressive against a really good hitting team. I keep seeing confidence building with each start. It’s cool to watch. It’s fun to catch when guys are taking command on the mound with a presence."

After giving up a leadoff homer to Tommy Edman in the third inning, Dunn retired the rest of the side in order.

“It’s starting to click," Dunn said. "It’s like I’ve been saying. Just get back in my routine, get back into the swing of things and get back to what I do well and understand myself. … Today was one of the best I’ve felt in those first three or four innings in a long time.”

Cincinnati's lineup picked up Dunn and then some in the bottom of the third with five hits to open the inning against Cardinals starter Dakota Hudson. Romine provided the lead with a two-run homer to right-center field. Jake Fraley delivered an RBI double inside the left-field foul line that scored Jonathan India from first base, and Kyle Farmer's RBI single made it a 4-1 game.

In the fourth inning, following Nolan Arenado's leadoff single, Dunn got Tyler O'Neill to ground into a double play, and Albert Pujols popped out in what proved to be Dunn’s final batter.

Even knowing his shoulder history, Dunn was not happy with the decision about being lifted and tried arguing to keep pitching.

"You obviously get a little nervous, but it feels different than what I went through in Seattle," Dunn said. "They were fortunate enough to make the right decision, so I am super thankful for D.B. and D.J. pulling me out. The competitor in me wanted to go, but God forbid I go out and throw one pitch and something worse happens and I’m out for another 460-whatever days. The competitor in me was pissed, but looking back at it now, it probably was the right move.”

With a rotation dealing with thin depth and several shorter outings, a lot has been asked of the bullpen lately, and it hasn't always been pretty. But the club's relievers retired 15 of 17 batters after Dunn departed.

It began with Derek Law, who made his Reds debut after being called up earlier in the day. Law pitched two innings, followed by one-inning outings from Joel Kuhnel, Buck Farmer and Alexis Díaz.

If Dunn recovers well enough to make his next start, the Reds will have dodged another setback. Starters Hunter Greene, Graham Ashcraft and Robert Dugger are among 18 players on the injured list for Cincinnati.

"I know [Dunn] wanted to stay in the game. It was a decision we made in his best interest," Bell said. "I think that's also a good sign. He was fighting a little bit to stay in after I made the decision. That makes me even more confident that he's going to be fine and keep going in the right direction."