CHICAGO -- The Houston Astros called up five players from Triple-A Round Rock on the first day of roster expansion on Monday.

The team recalled pitchers Jack Cassel, Fernando Nieve and Alberto Arias, along with catcher J.R. Towles, and purchased the contract of infielder Edwin Maysonet .

Towles has played in 50 games for the Astros this season, hitting .143 with four homers and 16 RBI. He was hitting .304 with seven home runs and 28 RBIs in 48 games for Round Rock.

Maysonet, who will be making his first major league appearance, hit .271 with six homers and 34 RBIs at Round Rock. Arias, who was claimed off waivers from Colorado, had a 2.63 ERA in 12 appearances with the Rockies.

Cassel is 2-2 with a 5.40 ERA in 11 career appearances, including seven starts. He was 9-5 with a 3.69 ERA in 19 games for Round Rock. Nieve, who went 2-5 with a 5.72 ERA in 36 appearances for Round Rock, is 0-1 with a 18.00 ERA in four games with the Astros this season.

Manager Cecil Cooper said Cassel and Nieve would both be used in middle relief.