KANSAS CITY -- The Astros called up right-handed pitcher Francis Martes, ranked as their No. 1 prospect by MLBPipeline.com, on Thursday. Martes is expected to help the beleaguered bullpen in a long relief role.
Martes was scratched from his scheduled start for Triple-A Fresno on Wednesday night, and was told he was joining the Astros.
"I didn't believe it," Martes said before the series finale against the Royals. "I didn't think I was going to get called up until all the players came up to me and said, 'Congratulations!'"
Martes, 21, hasn't pitched well this year at Fresno, going 0-2 with a 5.29 ERA in eight starts. In 32 1/3 innings, he's allowed 40 hits, 28 walks, five homers and struck out 38 batters. Martes has a 2.10 WHIP and opponents are hitting .299 against him.

"We're fortunate that we brought him up," manager A.J. Hinch said. "It's a guy who has great stuff, high-end stuff if he can get in the strike zone. He's had some trouble inside the strike zone, or finding the strike zone in Triple-A, but this level can make him raise his standards a little bit. I'll put him in the bullpen today and he's available for as many pitches as he would have had as a starter, and we'll have him in that role moving forward."
The Astros were forced to start reliever Dayan Diaz in a 7-5 loss to the Royals on Wednesday, and Houston wound up using five pitchers in a game in which lefty Dallas Keuchel was scratched minutes before the first pitch. Keuchel was placed on the 10-day disabled list with neck discomfort.
Even before Wednesday's game, the Astros' bullpen had been taxed as a result of starters routinely not pitching deep into games, with the exception of Keuchel and Lance McCullers With three starters on the disabled list -- Collin McHugh, Joe Musgrove and Charlie Morton -- long reliever Brad Peacock has been moved to the rotation and No. 4-ranked prospect David Paulino has made two starts.
Martes was acquired along with outfielder Jake Marisnick and infielder Colin Moran in the deal that sent pitcher Jarred Cosart, infielder Enrique Hernandez and outfielder Austin Wates to the Marlins on July 31, 2014.
Martes' fastball sat in the upper 80s when he signed out of the Dominican Republic for $87,000 in 2012, rose to the lower 90s in '14, and now operates at a consistent 93-95 mph, with a peak of 98. His breaking ball improved even more significantly last year, becoming a devastating power curveball. Martes' changeup is developing.
Last year, Martes went 9-6 with a 3.30 ERA in 25 games (22 starts) at Double-A Corpus Christi, striking out 131 batters in 125 1/3 innings. He was named a Texas League All-Star and also was an All-Star in the Arizona Fall League.