The 63-year-old Baker was greeted by a rousing ovation during pregame introductions from an orange-towel-waving sellout crowd of 43,492. The main center field scoreboard read "WELCOME BACK DUSTY GREAT TO SEE YOU BACK IN THE DUGOUT."
Baker has vowed this team is something special — "They love each other and they hang together," he said.
The Reds had dropped seven straight playoff games dating to 1995, when now-Nationals manager Davey Johnson and Cincinnati were swept in the NL championship series by Atlanta.
"I swear, I don't know any of these numbers," Baker said when it came up before the game. "You can't do anything about the last 17 years, whatever it is."
Latos began the third, working in relief for the first time since the minors, after pitching five innings Tuesday at St. Louis. While he had been set to go Game 3 on Tuesday in Cincinnati, the Reds said Cueto is day to day and certainly are hoping he'll be ready later this series.
"He didn't give us any sense of doubt he could do it," Price said of Latos.
Posey homered to left leading off the sixth for San Francisco, drawing cheers of "M-V-P! M-V-P!" for the NL batting champion. It was his second career postseason home run and gave him a six-game postseason hitting streak dating to his 2010 Rookie of the Year season.
Cain was left to watch at that point, and he hardly looked happy visiting with manager Bruce Bochy in the dugout after being pulled before the bottom of the fifth for George Kontos.
The right-hander went 23 1-3 postseason innings without allowing an earned run, fifth-longest in major league history.
But two of Cain's five defeats this season were lopsided losses against the Reds — 9-2 and 5-0 — in which he allowed a total of four home runs, eight earned runs and 16 hits in 13 innings.
He had everything in his favor, pitching from the very mound where he tossed the first perfect game in franchise history June 13 against the Astros. He won his final six decisions of the regular season dating to a loss at St. Louis on Aug. 6.
The Reds survived third baseman Scott Rolen's throwing error that allowed Hunter Pence to reach starting the fourth. Brandon Belt lined into a double play moments later and Latos got out unscathed.
Chapman put runners on first and second in the ninth and Baker paid him a visit. One out later he walked Marco Scutaro before the Giants scored on a wild pitch. Posey struck out to end it.
Now, the Reds hope to get Cueto back later this series.
The right-hander threw a second strike to No. 2 hitter Scutaro and walked off the mound in obvious pain. A trainer and Baker rushed out to check on him, and Cueto came out moments later.
He retired leadoff man Angel Pagan on a strikeout. During the at-bat, Pagan stepped out of the batter's box and was granted time. Cueto apparently didn't see it and continued his motion. But Baker said Cueto had felt some discomfort before the game and was alerted by Price.
He threw eight pitches and six strikes for the earliest postseason exit by a starter since Atlanta's John Thomson lasted one-third of an inning in Game 3 of a 2004 NL division series against Houston. Thomson came out with a sore muscle in his left side.
"You hated to see anybody lose their starter, but they brought in a good one, too," Bochy said.
NOTES: Bruce is .533 (8 for 15) lifetime vs. Cain. ... San Francisco won Game 1 in each of its 2010 series — the division series against Atlanta, NLCS vs. Philadelphia and the World Series against the Rangers. ... The franchises faced each other in the playoffs for the first time.