The Padres' second batter of the game, Tony Gwynn, was the first of four batters to reach via hit. The fourth was the most impactful: With two outs recorded in the second, Padres pitcher Tim Stauffer smacked Cain's 35th pitch of the game up the middle, hitting Cain in the right elbow. The sequence likely will cost Cain an appearance in his first All-Star Game.
Cain suffered a contusion -- X-rays were negative and ruled out a fracture -- as the ball hit him just below his throwing elbow, leaving him numb until a half-hour after he left the game. The 38,112 in attendance needed equal time for recovery after the 10-game winner's shortest career start.
Manager Bruce Bochy, joined by pitching coach Dave Righetti and trainer Dave Groeschner, immediately huddled with the right-hander behind the mound after the play. Bochy had already made the decision to lift Cain before his one practice pitch sailed over the head of catcher Eli Whiteside and hit the net behind home plate.
"I was letting him fight out there a little bit," Bochy said. "That's a pretty good shot he took. ... There was no question he was coming out."
Minutes after Bochy told reporters Cain was "doubtful" to pitch in Tuesday's Midsummer Classic, the pitcher used the antonym, while admitting the necessity of caution.
"It's probable," said Cain, who will attend the festivities in St. Louis even if he's unable to pitch. "I'm going to try to stay more hopeful than 'doubtful.' It'd be great to go and throw [Tuesday], but for the situation we're in here, playing ball real well, it'd be better to take that time and get it right."
The uncertainty accompanying Cain's injury was all that dampened the Giants' series-clinching win against the Padres, which pushed their record (49-38) a season-high 11 games above .500.
Cain's counterpart, Stauffer (0-1), retired the first 10 batters he faced but found trouble in the fourth against Pablo Sandoval. The Giants' No. 3 hitter homered on a first-pitch fastball for the second time in two nights (his 15th this season), driving in Randy Winn for San Francisco's 2-0 advantage.
The Giants led off the sixth with two hits (Fred Lewis' pinch-hit single and Aaron Rowand's double), but Stauffer intentionally walked Sandoval and retired the next two hitters to end the threat.
Bochy said opponents will likely be deterred from voluntarily issuing a free pass to Sandoval when cleanup hitter Bengie Molina returns to the lineup; Molina missed his second straight game attending to his wife, who gave birth to the couple's child before Saturday's game.
Stauffer was gone when San Francisco loaded the bases in the eighth on three straight singles from Winn, Sandoval and Travis Ishikawa but came away with no insurance runs. The Giants didn't require them, anyway, because the Padres' lineup collected just three hits in 7 1/3 innings against Giants relievers, compared with four against Cain.
"We hit Cain pretty good at the beginning, but when he left, it became a little tougher because our game plan was for Cain, and he throws a lot of fastballs," said San Diego's Edgar Gonzalez, who went 1-for-4. "They brought in the other guy, and he was throwing a lot of off-speed pitches. I don't think that we made good adjustments."
Bochy called on five of his seven relief pitchers, bookended by righties Justin Miller and Brian Wilson. That "other guy" was Miller (2-1), who logged 3 1/3 scoreless innings after Cain's exit. He lowered his ERA to 1.98 and leads the bullpen in frames pitched, with 41.
"The starting staff has taken innings away from us all year in a very positive way, so anytime we can go out there and try to perform and pick up the team," Miller said.
Everth Cabrera manufactured the Padres' lone run against Sergio Romo and Jeremy Affeldt in the eighth. Cabrera doubled, stole third base and scampered home on Whiteside's throwing error. Wilson entered the game with the potential game-tying run on first base and got a four-out save, his 23rd this season, by whiffing three.
"You don't win a game like that unless your bullpen comes through for you," Bochy said. "You lose one of your horses in the second inning, that's a big blow for your club. You need your bullpen to step it up, and they all did."
Andrew Pentis is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.