Brandon Waring hit a two-out homer in the ninth off Troy Patton to knot the score. Patton will serve a 25-game suspension at the start of the season after a positive test for a banned amphetamine.
Chen gave up one run, walked one and struck out three. He's got a 2.00 ERA in three outings this spring training.
Tommy Hunter, poised to take over for Jim Johnson as Baltimore's closer, worked a perfect fifth inning with a strikeout. The only two runs he's allowed in four innings came on solo home runs by Boston's Will Middlebrooks.
''I would prefer not to be in those situations, but they're definitely going to happen and I thought that was good damage control,'' Pelfrey said.
Orioles: Chen said he's on target for the start of the regular season.
''I think everything is on pace according to the plan,'' the left-hander said through an interpreter. ''Maybe some of my off-speed offerings I need to work on for a little bit. But everything else is in place for getting ready for the opening series.''
Manager Buck Showalter said: ''"He's in a good spot. Hopefully he can take this and build on it. He was scheduled for 60 pitches, and we had him 60 on the button. Just what the doctor ordered.''
Twins: Pelfrey allowed one run, five hits and one lamentable walk in 3 1-3 innings.
''The one thing that maybe irritated me more than anything was the (Nolan) Reimold at-bat, when I got ahead and tried to throw some sliders and got into a full count and walked him,'' Pelfrey said.
The walk, sandwiched between two singles, led to Baltimore's only run off the right-hander.
Pelfrey likes where he stands just over two weeks before the opener.
''I have three more starts and I want to take advantage of that,'' he said. ''I feel like there's still some arm strength to build up, but I feel good about where I'm at right now.''
The Orioles optioned right-handed prospect Dylan Bundy to Double-A Bowie.
Bundy, returning from ligament-replacement surgery in June, will continue his recovery in Baltimore's minor league camp in Sarasota.
''My arm is great,'' Bundy said. ''It just changes where I'm going to be.''
He could throw off a flat mound for the first time next week, Showalter said, adding that the session could take place in Baltimore's big league camp.
The Orioles now have 46 players at major league spring training, including nine non-roster invitees.
Showalter said of Lough: ''I don't know for sure what's going on with it. His neck has been stiff, hasn't felt quite right the last couple days. Decided to not take any chances with it.''
Casilla earlier missed time this spring with a strained right hamstring. The non-roster invitee is hitless in five at-bats, and his lack of playing time is hurting his chances of making the club.