Far from showing any jitters, the 26-year-old is 7-2 with a 3.36 ERA and has tossed seven quality starts.
Four of those have come at Camden Yards, where Chen will square off against the Nationals and right-hander Edwin Jackson on Saturday.
While he's 4-0 with a 2.72 ERA at home this season, Chen has also been piling up wins on the road. He did so on Sunday against the Braves at Turner Field, tossing seven scoreless innings and surrendering only six hits.
"He came over here basically without a changeup and a lot slower to the plate," manager Buck Showalter said. "[Pitching coach Rick Adair has] done a great job getting him some more weapons to defend himself at this level. He's a quick learner. He's grasping very quick."
Jackson, meanwhile, is coming off an inefficient start on Sunday against the Yankees.
While Jackson managed to give up just two runs on seven hits in six innings, New York took a patient approach at the plate against the right-hander, elevating his pitch count to 60 pitches by the third inning. In all, Jackson threw 110 pitches for the loss.
"They made me work," Jackson said. "I threw over 100 pitches in six innings; that's what they're notorious for doing -- making the pitcher work the pitch count. All in all, I came off the field giving the team a chance to win. As a starter, that's your job."
Nationals: Johnson returns to Baltimore
After spending eight years with the Orioles as a player and two more as a manager, Nationals skipper Davey Johnson made his first appearance in Baltimore as a visitor on Friday.
"It feels really good," Johnson said. "It's a beautiful ballpark. I always loved coming here. I love the fans in this area."
Johnson played second base for the Orioles as a member of their World Series championship teams in 1966 and 1970 and returned to Baltimore as manager in 1996.
"I've always had good memories about winning and as a player, just the town more than the ballparks," Johnson said. "All of my memories in Baltimore and with baseball are great memories."
Washington signed third-round Draft pick Brett Mooneyham from Stanford on Friday, the team announced. In his junior year at Stanford, Mooneyham posted a 7-5 record and a 4.26 ERA, with 90 strikeouts and 37 walks in 82 1/3 innings. His father, Bill -- a first-round selection of the California Angels in 1980 -- appeared in 45 games for the Oakland Athletics in 1986.
Orioles: Reimold to have season-ending surgery
Orioles outfielder Nolan Reimold will undergo surgery to repair a herniated disk in his neck on Monday morning at Johns Hopkins Hospital, a procedure that will be performed by neurosurgeon Dr. Ziya Gokaslan. Such a procedure is expected to end the 28-year-old's season.
Reimold announced the decision prior to Friday's game and said he went back and forth on it a few times, but ultimately the consensus of multiple doctors won out.
"The best thing to do as far as my career was definitely to get the surgery," Reimold said. "[It will] get the pressure off the nerve that's getting pushed on."
The Nationals are 9-7 in Interleague Play this season and can post a winning record against the American League for a second straight year by winning at least once against the Orioles this weekend.
The Orioles are 10-3 at home against the Nats since 2008.