The Mets needed an extra arm after playing a two-ballpark doubleheader against the Yankees on Friday. Mike Pelfrey was next in the rotation but he would've been pitching on three days' rest, so the Mets opted to go with 13 pitchers for the time being.
Armas was 5-7 with a 2.54 ERA in New Orleans after signing a minor league contract in February. He was 4-5 with a 6.03 ERA in 15 starts and 16 relief appearances last season with the Pirates.
Infielder Andy Phillips, batting .154 in 26 at-bats with four RBI, was designated for assignment. The Mets claimed Phillips off waivers from Cincinnati last week.