Pineda will be opposed by Jason Marquis, who always takes some major hacks at the plate in Interleague Play.
A career .202 hitter during 12 seasons in the National League, Marquis has a .267 average, with eight hits -- including two doubles, a home run and six RBIs -- in 30 Interleague plate appearances.
While Marquis may be ready at the plate, he better bring his A-game to the mound against Pineda.
The Mariners' right-hander carried a no-no into the sixth inning last week against the Phillies, only to have it broken up with two outs in the sixth.
The talented rookie wound up tossing six innings, giving up one run on two hits for the win. Walking three and striking out five, Pineda improved to 7-4 on the season with a 2.64 ERA.
"Pineda was good. Real good. Very good," Philadelphia manager Charlie Manuel said after the game. "He looked like he was getting a little spent there, but he was really good. We didn't hit too many balls hard against him the first five or six innings."
While Marquis leads Washington in the win column with eight, he received a no-decision in his most recent start on Friday against the Orioles. The right-hander battled through 5 1/3 innings, allowing four runs on 12 hits. Marquis (8-4, 3.86 ERA) also struck out three and walked none.
Over his career, Marquis is 10-8 with a 5.78 ERA in 25 starts during Interleague Play.
Mariners: League feeling better after calf injury
After taking a line drive off his right calf that forced him to exit Tuesday's game, Brandon League felt much better Wednesday.
League threw on flat ground and in the bullpen Wednesday during batting practice under the supervision of pitching coach Carl Willis. While he was sore, League no longer walked with a limp.
"He's a little better than we thought he would be," manager Eric Wedge said.
Rookie second baseman Dustin Ackley received his first day off Wednesday after his Friday promotion from Triple-A Tacoma.
Wedge said that the left-handed-hitting Ackley will continue to be an everyday player against righties and lefties, but just wanted to give him a day off.
Nationals: Riggleman weighs DH options
With the Nationals going on the road to face American League teams starting Friday, manager Jim Riggleman is deciding whom to select for the designated hitter role.
He's already indicated that Matt Stairs will likely face right-handed pitching, yet many Nats regulars could see some time in the DH spot.
"I may pick a day or two to give a position player a rest and let them DH, and have somebody else play their position, whether it's [Jayson] Werth or [Danny] Espinosa, guys who are pretty much playing every day." Riggleman said. "Sometimes, you like to let them be the DH and keep them swinging the bat, but they don't have to take on everything else."
Seattle's Jamey Wright is three appearances short of 500 in his career, with 246 having been starts.
The Mariners are 29-22 since April 26, the second-best record in the AL over that span. Seattle trails only the Red Sox, who have a record of 35-18 during that time.
The three-game series between the Mariners and Nationals marks only the fifth series between the two franchises, and the first since 2008.