ST. LOUIS -- Left-hander Reiver Sanmartin was usually all smiles when this season began. Then, the rough outings came and didn't stop.

By his last start on May 1 at Colorado, the smile was all but gone and Sanmartin's spirits were crushed. He was optioned to Triple-A Louisville after a 10-1 loss to the Rockies in which he gave up six earned runs on six hits while recording only two outs in the first inning.

On Sunday, Sanmartin was back in the big league clubhouse again, after being added to Cincinnati's taxi squad.

"I take it as a good sign," Sanmartin said via translator Jorge Merlos. "I’ve been working really well in the bullpen, and obviously, that’s why I got called up to be here for any type of work."

Sanmartin could be activated as soon as Monday to join a Reds bullpen that has been taxed, hard hit and struggling to get outs. He would provide a different look -- not just by being a lefty but one that throws a lot of changeups and lacks power stuff.

The Reds' road trip moves to Arizona for three games, beginning on Monday.

Initially a starter when he went back to Louisville, Sanmartin's past three games were all in relief roles. Over his past two appearances, totaling 2 1/3 scoreless innings, the 26-year-old has allowed one hit and no walks with seven strikeouts.

"In reality, it was me working on my mind, my mentality. I really had to work on that over everything," Sanmartin said. "I just had to tell myself I had to be the same pitcher I was before. That way, I can get back to my usual rhythm and how I was beforehand."

In two starts at the end of last season for the Reds, Sanmartin was 2-0 with a 1.54 ERA. As the rotation was decimated in Spring Training by the trade of Sonny Gray and injuries to Luis Castillo and Mike Minor, Sanmartin pitched well in camp and earned a spot. In five games, including four starts, he was 0-4 with a 13.78 ERA. The one game he didn't start, the Reds used an opener.

Manager David Bell saw Sanmartin on Sunday morning and noticed the difference from the pitcher who was in his office getting demoted five weeks ago.

"You can see it in his face. I just saw him," Bell said. "The last time I saw him was in Colorado on a tough day for him. He definitely has his smile back. He has been pitching well and has his confidence back. That’s so important. He has everything else he needs."