WASHINGTON -- Nationals pitching coach Randy St. Claire went to the Arizona Fall League recently to check on pitching prospects Adam Carr, Ross Detwiler, Cory Van Allen and Zechry Zinicola.

St. Claire worked with the hurlers for four days and was convinced they will be in the big leagues some day.

"They threw the ball great," St. Claire said. "I did side work with them. They did a real nice job."

With that in mind, MLB.com asked St. Claire on Wednesday night to give his take on all four pitchers.

Carr: The right-hander had a rough season for Class A Potomac and Double-A Harrisburg in 2008, but he is showing signs of improvement in the AFL, giving up one run in 8 1/3 innings for the Peoria Saguaros. It helps that Carr fixed his mechanics.

"He made a lot of progress," St. Claire said. "He has settled down and his delivery is a lot more controllable. His control is a lot better. He has made progress for a kid who hasn't pitched much."

However, St. Claire said he would like Carr to increase the velocity on his slider and have more control of the pitch.

Detwiler: The left-hander had an up-and-down season for Class A Potomac this past season, but he has yet to give up a run in seven innings for the Saguaros. According to St. Claire, Detwiler is not throwing the ball across his body as much as he did when he was drafted by the Nationals in 2007. The Nationals want him to throw the ball on a straight line.

"He has been working very hard on keeping his lines to where he can [throw the ball on] both sides of the plate," said St. Claire. "Ross commanded the ball pretty decently. It was really nice to see him make that adjustment. I know he is working hard at it. That is something it takes a little while to correct. He was a little inconsistent with the curveball. He did throw some good ones, however."

Van Allen: Of the four pitchers, Van Allen is having the roughest time in the AFL, giving up 12 earned runs in 9 2/3 innings. However, St. Claire believes Van Allen could be another John Lannan-type of pitcher who is able to locate all of his pitches. He did have some difficulty with his delivery when he was out of the stretch.

"He is pretty quick to the plate and, at times, I think he wants to be too quick. His arm drags and he elevates the ball," St Claire said about Van Allen's delivery.

Known as a fastball and changeup pitcher, Van Allen has added a slider to his repertoire. St Claire said the pitch has come a long way since Spring Training.

Zinicola: The right-hander has shown so much progress with his mechanics that St. Claire told general manager Jim Bowden that he would like to see Zinicola get an invitation to Spring Training. It helped that St. Claire saw Zinicola throw split-fingered fastballs that struck out two left-handed hitters in the AFL. Zinicola set up those hitters by using his fastball and slider to get ahead in the count.

"I saw him pitch twice and he threw [exceptionally well], especially the second time after we worked on a couple of little things," said St Claire. "I don't know if they are inviting him to Spring Training, but I told Jim I would love to see him in Spring Training. He really impressed me."