Fortunately for him, he gets to face baseball's worst team again Monday night.Walker is set to make what will likely be his final start of the year as the Seattle Mariners open a three-game home set against the Astros.Considered one of the league's top prospects, Walker (1-0, 3.60 ERA) has provided Mariners fans with a glimpse of the future. The 21-year-old right-hander showed off his stuff Aug. 30 in a 7-1 victory at Houston, yielding one unearned run and two hits in five innings."He was really impressive," Astros outfielder L.J. Hoes said of the 6-foot-4 Walker. "He's a big kid. On his video, he didn't look as big as he really is. It says he's throwing 96 (mph), but it seems way harder than that because he's so big."Walker started off strong Wednesday with three innings of no-hit ball before allowing four runs in the fourth in a 6-4 win at Kansas City. He came back out to throw a 1-2-3 fifth but didn't factor in the decision."In the fourth, he just came up in the zone a little bit," manager Eric Wedge said. "I was glad to see him get through it. And then I was really happy to see him out there in the fifth and pitch another inning for us. I felt it was important to go out in the fifth. That proves something to him. We know he can do it."I love his repertoire of pitches and the way he works, his cutter and his breaking ball off his fastball. The changeup will continue to come, too."Though it wasn't his best showing, Walker earned high praise from Royals manager Ned Yost."You can see what all the hype was about," Yost said of Walker, who is on an innings limit and expected to be shut down following this start. "He's got a free and easy power arm. He's a good talent."Walker now turns his attention back to the Astros (47-96), who have dropped 10 of 13. Houston is looking to avoid a fourth consecutive loss after going 1 for 14 with runners in scoring position during Sunday's 7-2 defeat at Oakland.The Astros will try to bounce back behind fellow rookie Jarred Cosart (1-1, 2.13), who exited Tuesday after throwing a season-low four innings in a 9-6 loss to Minnesota. The 23-year-old right-hander gave up a season-high four runs on a pair of two-run homers."It's kind of what everyone's been waiting for," said Cosart, who had been taken deep once in his first eight starts. "I didn't get the results. A starter's job is to keep the team in the game and give us a chance to win the game. I didn't do that."Cosart could bounce back on the road, where he is 1-1 with a 1.38 ERA in six outings. He has surrendered one or zero runs in five of those games.Cosart will be making his first appearance against the Mariners (65-78), who were denied a three-game sweep by Tampa Bay with a 4-1 loss Sunday. Seattle is hitting .172 with runners in scoring position during a 6-11 stretch.The Mariners have taken eight of 10 from Houston.