Carlos Delgado was 3-for-3 with two doubles, ending a 1-for-13 slump, and Ryan Church had two hits and an RBI. Castro, a backup catcher, has 11 RBIs in 59 at-bats.
Rick Ankiel hit a two-run homer and Aaron Miles hit in his 13th straight game for the Cardinals, who won 7-1 on Monday in the opener of a four-game series but have lost nine of the last 12 regular season meetings against the Mets.
Armas (1-0) was leading the PCL with a 2.54 ERA when the Mets purchased his contract from Triple-A New Orleans to fill a rotation spot created by a rainout followed by a doubleheader last week.
He's 3-0 with a 3.10 ERA against the Cardinals the last two seasons and 3-0 for his career at 3-year-old Busch Stadium after allowing four runs in six innings.
Billy Wagner got three outs for his 19th save in 23 chances.
Five of the first six Mets reached against Wellemeyer (7-3), although New York managed only one run the first two innings on Damion Easley's RBI groundout in the second. Jose Reyes was caught stealing and Endy Chavez got caught in an inning-ending rundown between third and home in the first when a likely wild pitch bounced off the concrete wall behind the plate and went right back to catcher Yadier Molina.
Ankiel's 16th homer gave the Cardinals the lead in the first and Skip Schumaker's RBI double in the second made it 3-1.
Castro's two-run double tied it in the fourth, Church's RBI highlighted a three-run fourth and Wright's homer made it 7-3 in the sixth. Wright has four homers and 16 RBIs in his last 15 games.
Mets reliever Duaner Sanchez was struck in the right leg by a line drive by Molina in the eighth. The ball deflected to Wright at third base, who threw to first for the final out of the inning.
Sanchez limped off the field after receiving medical attention.
