The Missions completed their mission on Sunday night, ensuring a spot in the Texas League playoffs this fall.
Former first-round pick Jaff Decker scored the decisive go-ahead run and closer Brad Brach struck out two in the ninth for his 16th save as Double-A San Antonio clinched a playoff berth with a 6-4 win over Midland, winning the Texas League's South Division first-half title.
San Antonio (42-19) also needed a win from Midland, which defeated Frisco, 9-2. The Missions, who last claimed the first-half title in 2009, when the team went 39-31, will host the first two games of the Texas League postseason's first round Sept. 7-8 at Wolff Stadium.
It was the 24th win of the year at home for San Antonio, which has treated its fans to a 24-5 record at Wolff Stadium this season.
The San Diego affiliate sent 2010 Futures Game All-Star Simon Castro to the mound, but the right-hander was pulled after allowing four runs on five hits and 79 pitches over five innings. Considered one of the Padres' top right-handed prospects, Castro ran into trouble in the fifth when he allowed Midland to tie the game on three straight run-scoring hits to Jonathan Villar, Jimmy Paredes and Jose Altuve.
San Antonio took a 4-0 lead in the first when James Darnell hit a two-run double, Beamer Weems lined an RBI double to center and Vincent Belnome scored on a sacrifice fly.
Anthony Contreras delivered the go-ahead hit in the eighth when he singled home Decker off Shane Wolf. Ali Solis followed with an RBI single to plate Beamer Weems for a 6-4 edge.
Nick Vincent (1-0) got the win after pitching a perfect eighth inning in relief before Brach caught Federico Hernandez and T.J. Steele looking to finish it off.
Brach, 25, was the California League's 2010 Pitcher of the Year and MLB.com's Class A Advanced Relief Pitcher of the Year after collecting 41 saves and five wins.
Lefty Xavier Cedeno started for Corpus Christi and was charged with four runs on five hits over five frames.