Cueto is 17-9 with a 2.79 ERA and the Giants are 22-9 when he starts. Bumgarner is 14-9, 2.71 after Saturday night's 9-6, 10-inning win over the Padres at Petco Park, improving San Francisco to 20-14 in his turns.
Cueto was scheduled to start in Sunday's finale of a four-game series against the Padres, but rookie left-hander Ty Blach will take his place.
Giants manager Bruce Bochy officially announced Saturday what everyone expected: The groin injury that Cueto suffered in his last start would prevent him from pitching Sunday. He will probably miss only one start.
The Giants go into Sunday tied with the New York Mets for the top spot in the National League wild-card race. The St. Louis Cardinals trail the Mets and Giants by one-half game. San Francisco is eliminated from NL West contention with a loss or a Dodgers' victory at home over Colorado.
Blach gets the call to face resurging veteran left-hander Clayton Richard, who is 3-2 with a 1.87 ERA in nine games (seven starts) since rejoining the Padres on Aug. 6 following a three-year absence from San Diego and Petco Park.
Richard, who is throwing from a new arm slot with a sinker added to his repertoire, has already faced the Giants since his return to the Padres. On Sept. 13, he held them to three runs on 11 hits and three walks in 5 2/3 innings at AT&T Park. That was one of five straight games the Padres have won with Richards starting.
"Clayton's put himself in our plans moving forward," Padres manager Andy Green recently said of the 33-year-old.
"Ty has started more recently then either Peavy or Cain," Bochy said. Blach has made two, three-inning appearances for the Giants since being promoted from Triple-A Sacramento.
Blach was 14-7 with a 3.43 ERA in 26 starts with Sacramento. His 14 wins tied a Sacramento franchise record. With San Francisco, Blach has allowed one hit over six scoreless innings with a walk and a strikeout.
Blach should be familiar with half the starters deployed by the Padres on Sunday.
Catcher Austin Hedges, right fielder Hunter Renfroe (who hit his first major league homer Saturday night off Bumgarner), center fielder Manuel Margot (who had his first major league hit and RBI on Saturday) and second baseman Carlos Asuaje all faced Sacramento while members of the Padres' El Paso affiliate that won the Pacific Coast League title.