Southpaw prodigy Dallas Keuchel makes the third start of his big league career tonight when the Houston Astros entertain the San Diego Padres in the finale of a four-game series at Minute Maid Park.

Keuchel, a seventh-round draft pick in 2009, signed and began his pro career at Single-A before moving to the Double-A level a year later. He split 2011 between Double- and Triple-A and made 13 starts with Triple-A Oklahoma City this year before arriving in the majors in mid-June.

He was called up when righty Bud Norris began a stint on the 15-day disabled list, but will maintain his starting status while the team experiments with a six-man rotation with no off days before the All-Star break.

Keuchel allowed a single run on four hits in five innings while getting a no- decision against Texas in his debut on June 17, then went the nine-inning distance with six hits and a run allowed while downing Cleveland, 8-1, in start No. 2 on June 23.

Now 24, the Tulsa, Okla. native posted a 3.85 earned run average, walked 99 batters and struck out 314 batters in 475 minor-league innings from 2009-2012.

He'll opposed by 25-year-old righty Andrew Cashner, who'll start for the second time this season and the third time overall in his 89th big league appearance.

The Texas Christian University product signed with the Chicago Cubs after they selected him 19th overall in the 2008 draft, then pitched in 60 games over two seasons before coming to San Diego in a four-player trade on Jan. 6.

He made 27 straight appearances out of the bullpen before starting on June 9 at Milwaukee and allowed a run on two hits in 2 1/3 innings of a game the Padres won, 5-2.

Cashner has since made three starts at Double-A San Antonio of the Texas League and was 2-0 with a 1.88 ERA across 14 1/3 innings, walking three and striking out 22.

He's 2-1 against the Astros in eight career relief appearances.

On Wednesday, Lucas Harrell was helped by a big defensive play in the ninth inning to record his first career shutout as the Astros blanked the Padres, 1-0.

Harrell (7-6) scattered six hits and four walks with seven strikeouts, while Matt Downs supplied the offense with a home run for Houston, which won for the fourth time in five games.

"What a great job working around those six hits," Astros manager Brad Mills said. "To see a guy throw like that and do such a great job, that's nice to see."

Clayton Richard (5-8) allowed just two hits and a run over seven strong innings to take the loss and snap a three-start win streak.

Yonder Alonso and Logan Forsythe each collected a pair of hits for the Padres, who dropped their second straight game.

San Diego won five of eight games with the Astros in 2011 and five of seven in 2010. Houston last won the season series between the teams in 2009, taking six of seven games.