SAN DIEGO -- Nationals right-hander Stephen Strasburg was at PETCO Park on Friday afternoon and had a bullpen session without any problems. Besides throwing fastballs off the mound, Strasburg threw changeups while playing catch on flat ground.

Pitching coach Steve McCatty, who watched Strasburg pitch for the first time since Spring Training, said Strasburg looked effortless and his mechanics looked fine.

"He is always in good spirits," McCatty said. "This kid is mentally tough. He knows what the road was planned out for him last year and what he had to do. He is doing a great job of it."

While everyone is talking about the one-year anniversary of his debut, Strasburg is thinking about getting his elbow healthy after undergoing Tommy John surgery last September. He currently has three bullpen sessions a week and throws 30-40 fastballs per session.

Strasburg hopes to pitch in a Major League game sometime in September.

Mattheus promoted as Kimball lands on DL

SAN DIEGO -- The Nationals selected the contract of right-hander Ryan Mattheus from Triple-A Syracuse and placed right-hander Cole Kimball on the 15-day disabled list with right shoulder inflammation.

Mattheus posted two saves and 10 scoreless innings during nine relief appearances with the Chiefs. Including a 13-game stint with Double-A Harrisburg, Mattheus is 2-1 with six saves and a 1.46 ERA in 22 appearances in 2011.

Mattheus, 27, is 3-2 with six saves and a 1.25 ERA in 32 games since returning from July 2009 Tommy John surgery on July 31, 2010.

Mattheus was sleeping around 10 a.m. ET., when he received the call from Syracuse manager Randy Knorr about his promotion. Mattheus said the call was the best he has ever received. The day was even better when he called his parents and sister to give them the good news. They are already in San Diego to watch Mattheus play. Mattheus didn't arrive at PETCO Park until around 7:30 p.m. PT.

"It's a great feeling," Mattheus said. "I was still in bed. I woke up to about three, four missed calls from my manager -- Randy Knorr. I answered the phone and he said, 'Hey, get out of bed, get yourself packed. You are going to the big leagues.' I was pretty excited. I wasn't expecting it at all. It was out of the blue. It was amazing."

Mattheus was acquired from the Colorado Rockies on July 31, 2009, just weeks after his ligament-replacement surgery, as part of a three-player trade that sent left-handed pitcher Joe Beimel to Colorado. He is 32-42 with 23 saves and a 4.93 ERA in 193 games (88 starts) during his career.

"I battled Tommy John surgery that I had in 2009," Mattheus said. "It definitely hasn't been the smoothest sailing so far."

As for Kimball, he told the team after Thursday's game against the Padres that his shoulder was hurting. Kimball said he took an MRI and hopes that there isn't anything worse inside the shoulder. Kimball revealed that his shoulder has been hurting him since April.

"If you are hurt, you have to say it," manager Jim Riggleman said. "You are going to make it worse -- a sore area that might become a little painful that now becomes a real injury."

Kimball's numbers don't indicate that that he was injured. Kimball, 25, was 1-0 with a 1.93 ERA in 12 games with Washington this season.

"If I kept pitching through it, I might have something bad happen," Kimball said. "Right now, it's some major inflammation. I took some anti-inflammatories, I'll get some rest, start throwing again and get back where I was.

"It's very disappointing. It happens to a lot of guys. At least it's not surgery or something major at this point."