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Lucas Harrell will try to lead the Houston Astros to their first ever victory in Baltimore on Tuesday night when he takes the mound for the opener of a three-game series with the Orioles.

Astros ace Bud Norris was slated to start this contest, but was a scratch on Tuesday afternoon. Norris is likely to join a recent long list of players dealt by Houston ahead of the non-waiver trade deadline, which is Wednesday.

Currently 34 games under .500 and 27 games out of first place in the AL West, the Astros are expected to be major sellers. They got things started on Monday, sending closer Jose Veras to the Detroit Tigers for minor league outfielder Danry Vasquez and a player to be named later.

Among those dealt by the Astros ahead of the trade deadline over the past few seasons include Carlos Lee, Brett Myers, Wandy Rodriguez in 2012, Hunter Pence and Michael Bourn in 2011 and Roy Oswalt and Lance Berkman in 2010.

Norris could join that list given his expected pay raise next season. He has been Houston's top starter all season, going 6-9 with a 3.93 earned run average in 21 outings, but is winless in his past three with an 8.47 ERA.

"It's something I've prepared myself for last night and the days leading up to it," Norris told Houston's website of possibly getting traded after last Wednesday's no-decision versus Oakland. "It's definitely a little emotional, too. I just went out there and threw the best ballgame I could and give my team a chance to win.

"It's a challenge for sure. There's a lot going on, but you have to go out there and keep your focus and just go out there, play the game and pitch."

Harrell steps in tonight in place of Norris and is just 5-10 with a 5.17 ERA in 23 games (19 starts) this season. Houston has lost each of the past seven games that the right-hander has appeared in, with Harrell getting charged with three losses over that span.

Harrell last pitched on Thursday, giving up three runs over three innings at Toronto, and lost his only other career start versus Baltimore. That came on June 4, though he only allowed one unearned run over seven innings.

That 4-1 win by Baltimore came in the opener of a three-game series in Houston. The Orioles took two of three in that set and have won eight of the past nine meetings between the clubs. Baltimore has never lost at home versus Houston, winning all six matchups.

The O's hope that trend continues as they were shut out 5-0 by the Boston Red Sox on Sunday, their fifth loss in six games. That leaves Baltimore five games out of first place in the AL East and just a half-game ahead of the Cleveland Indians for the league's second wild card.

"We're grinding right now, not going too hot," said Sunday's losing pitcher for Baltimore, Jason Hammel. "We're still playing close ball games. It's not like we're getting blown out."

Looking to get the Orioles on track tonight will be Wei-Yin Chen in his first ever meeting with the Astros. He was on the disabled list during the last meeting, part of a near two-month stint caused by a right oblique strain.

Chen is 2-0 with a 2.18 ERA in three starts since his return and has not lost since May 1. He has won three straight outings before not factoring into a 4-3 loss at Kansas City on Wednesday.

The 28-year-old southpaw yielded three runs over 7 1/3 innings and was touched for two homers, the first he allowed in five starts.

Chen is 5-3 with a 2.78 ERA in 11 starts this season, going 2-0 with a 1.86 ERA in three at home.

The Astros, who have lost 10 of 12 and 20 of their past 25, hope to have second baseman Jose Altuve in the lineup after a tight left quad held him out of Sunday's 2-1 loss in Toronto. He is hitting .280 in 97 games this season.