PORT CHARLOTTE, Fla. -- A bad outing against the Twins right before the 2018 All-Star break was the first time Diego Castillo felt a little uncomfortable at the big league level.

After displaying his 100 mph fastball that has sinking action and cruising through opposing lineups while posting a 1.74 ERA in his first 17 appearances in the big leagues, Castillo started to run into some trouble.

Castillo allowed three runs (two earned) in a July 15 game against Minnesota. That was followed with consecutive outings of giving up two earned runs against the Marlins and Yankees. From July 15 to Aug. 5, Castillo gave up 10 earned runs in just 8 1/3 innings of work. He saw his ERA rise from 1.74 to 4.34.

Part of his struggles, Castillo said, were because he grew concerned of a possible demotion back to Triple-A.

“I didn’t know my situation with the team,” Castillo said. “I didn’t know if I was only in the big leagues for a couple of days or if I was here for the entire season.”

Castillo said he got comfortable once he came to terms with the fact that he had struggled, and the Rays reassured him that he was a big part of what the team wanted to do last season and moving forward into the 2019 season.

“We saw enough at the end that I think he left the season feeling pretty good,” manager Kevin Cash said.

Cash said that it’s fair to assume that Castillo will serve as an opener -- which he did 11 times last season -- from time to time, but the team is hoping that he can also transition into becoming an important piece in late-inning situations.

“We can’t have an opener for everybody because we need to have guys to get outs in the seventh, eighth and ninth innings,” Cash said. “He showed plenty of consistency once he went into that [opener] role and then kind of transitioned out of it towards the end.”

Last season was a learning experience for Castillo. The blazing fastball will continue to be the money pitch for Castillo, but he made it a point to work more on his offspeed pitches over the offseason.

“I learned that to stay here in the big leagues, you just have to stay consistent,” Castillo said. “I worked harder this year. I focused on some of the pitches that didn’t give me good results sometimes. I just have to keep working on my pitches.”

Castillo is not sure what role he’ll have in the bullpen this season. He says that the experience of closing games in the Minor Leagues and starting games at the big league level will help him adapt to whatever role Cash and the Rays decide on.

“I definitely feel more comfortable than last season,” Castillo said. “They can put me in any situation and I’ll give my 100 percent. I’m ready for whatever comes.”