UPDATED 7:00 p.m.: The Nationals officially called up rookie right-handed reliever Abel de Los Santos from Class AA Harrisburg. De Los Santos, acquired along with minor league infielder Christopher Bostick in an offseason trade involving Ross Detwiler, has six saves, a 2.65 ERA with a 5-to-1 strikeout-to-walk ratio in 26 games with Harrisburg.

“I feel great here,” De Los Santos said. “It’s like the first day of school.”

In order to make room on the active 25-man roster, the Nationals optioned hard-throwing but struggling reliever Blake Treinen to Class AAA Syracuse. Treinen turned a one-run deficit to a five-run hole in the ninth inning on Sunday. Despite high-90s fastballs and strikeout stuff, Treinen has struggled with command and against left-handers. He has a 4.56 ERA along with 21 walks in 41 innings. He was an early season favorite to take over the eighth set-up role but has been relegated to long relief and now Syracuse to iron out issues.

“For Blake, it’s about consistency,” Manager Matt Williams said. “We know what kind of talent he’s got. It’s heavy sink coming out of his hand at 97, 98 mph. The issues that he has had with some left-handed hitters this year is something to work on. Yesterday was an example where he got ahead but he just couldn’t finish. We’ll get him an opportunity to get down there and get consistent work and get him stretched out if we can, be able to go out and throw three innings if we need him to do that. … He’s got tremendous stuff. He’ll go down and work hard and refine and be back quickly as far as I’m concerned.”

De Los Santos throws a fastball between 93-95 mph, allows few walks, hits and home runs and averages about a strikeout per inning. The 22-year-old native of the Dominican Republic is also capable of pitching multiple innings in a single outing. He has a max effort delivery but throws strikes, has a strong curveball and also throws a change-up. He converted from starting to reliever in 2013 in the Rangers minors and took well to it.

At first, de Los Santos tried to make an impression with his new organization this season by throwing hard. But his command wasn’t as sharp.

“The first few games I was too excited,” De Los Santos said. “I calmed down. I got into a good rhythm.”

De Los Santos has not allowed a run since June 8, a span of 15 innings in which he has held batters to a .104 average and struck out 15. His 0.884 WHIP (walks and hits per inning pitched) is fifth-best in the Eastern League. The Nationals major league coaching staff didn’t see de Los Santos in spring training but “everybody loves his stuff,” Williams said.

De Los Santos received the surprising news of his call-up on Sunday evening. Harrisburg was in Bowie and pitching coach Chris Michalak asked de Los Santos if he had any good clothes. De Los Santos said he did and Michalak told him he would look good in them in D.C. with the Nationals. De Los Santos first called home to tell his mother in Puerto Plata but she wasn’t home.

“She was very surprised,” de Los Santos said. “My sister couldn’t believe it.”

When De Los Santos pitches, he will become the 15th reliever used by the Nationals this season, five of them first-year relievers. From 2013 to 2014, the Nationals used only seven first-time relievers.

“It’s not ideal as you set out at the beginning of the season after spring training,” Williams said. “You’ve got your 25 guys and hope that they stay healthy and are with you for the whole season. We all are realistic and realize that’s never the case. So it’s going to be opportunity for you relievers and young position players to come and show what they can do. … For me, it’s understanding them and trying to get to know them as quickly as possible and when to insert them into a game to have success.”

Added de Los Santos: “I think it’s great they give us a chance to show what we can do. We, too, have talent and can do the job.”

In order to make room on the 40-man roster, the Nationals transferred Jayson Werth from the 15-day to 60-day disabled list. He has been on the disabled list since May 16 so he was eligible to come off the 60-day disabled list on July 15. Werth is progressing in his rehab assignment in his return from a fractured wrist and could be back by the end of the month. Moving him to the 60-day disabled list opened up a 40-man roster spot without forcing the Nationals to cut ties with a player now.