Chicago (23-34) at Houston (28-31)

With two of their starters on the disabled list and one of the best pitchers of all time still weeks away from joining the team, the Houston Astros are turning to a rookie.

Chris Sampson makes his first major league start when the Astros wrap up a three-game series with the Chicago Cubs at Minute Maid Park on Wednesday.

Sampson (0-0, 5.06 ERA) made his major league debut Friday, allowing three runs and six hits in 5 1-3 innings of relief without receiving a decision in Houston’s 14-3 loss to Cincinnati.

“It was indescribable,” said Sampson, who was recalled from Triple-A Round Rock earlier that day. “It happened so fast, I really didn’t have time to think.”

The Astros were forced to turn to the Pasadena, Texas native after placing starter Roy Oswalt on the 15-day disabled list with a mid-back strain, retroactive to May 30, and transferring starter Brandon Backe to the 60-day DL with a sprained right elbow on Tuesday.

“He did see some improvement,” manager Phil Garner said of Oswalt, a 20-game winner each of the last two seasons. “But I feel certain that if we go ahead and DL him that we’ll have him 100 percent when he’s ready to go on the 14th.”

Also on Tuesday, Roger Clemens threw 62 pitches—41 for strikes—and finished with six strikeouts over three innings during a tuneup for Houston’s Class-A team in Lexington, Ky.

The 43-year-old Clemens, who played alongside his son Koby, gave up a long home run but otherwise looked sharp. The seven-time Cy Young Award-winner will most likely start Sunday at Double-A Corpus Christi, Texas, and then June 16 at Round Rock.

He could return to the majors by June 22 against Minnesota.

“My arm is great,” he said. “One step down, two to go.”

Sampson will be opposed by fellow rookie Sean Marshall (3-3, 4.80). He allowed two runs and eight hits in 6 1-3 innings of the Cubs’ 14-inning, 5-4 win over the St. Louis Cardinals on Friday.

The left-hander had lost his previous two starts, allowing nine runs in 9 1-3 innings over that span.

“Lost in the game was Marshall’s effort,” manager Dusty Baker said. “He had a great game.”

Marshall, who is making his 12th start, has never faced the Astros.

Wandy Rodriguez pitched on three days’ rest Tuesday and threw seven shutout innings in Houston’s 4-1 win over the Cubs.

Lance Berkman homered and Chris Burke drove in two runs Tuesday for the Astros, who ended a five-game losing streak. Preston Wilson scored on Chicago starter Kerry Wood’s second-inning error, giving Houston its first lead since Wednesday against St. Louis.

John Mabry doubled in a run for the Cubs, who lost for just the third time in eight games.

Shortstop Ronny Cedeno went 0-for-4, ending his career-best 10-game hitting streak.