Two more games like this and they'll win the World Series.
Cain was sharp, the Rangers bullpen was not and San Francisco broke away for a 9-0 win Thursday night. The Giants headed to Texas with a 2-0 lead that looked to come way too easily.
Edgar Renteria reprised his October success with a go-ahead home run, and the Giants broke away with seven runs in the eighth, the biggest inning in their postseason history.
Texas relievers walked four straight batters with two outs in the eighth, letting the game out of control. At this rate, team president and part-owner Nolan Ryan probably wants to grab a ball himself and get on the mound.
Texas set a record for most runs allowed in a franchise's first two Series games.
"You take all the runs you can get," Giants manager Bruce Bochy said. "It's nice to have a cushion going into the ninth."
Cain drew frenzied ovations from a crowd waving Halloween-colored orange pompoms, a day after the Giants won the opener 11-7.
After scoring just 19 runs in the six-game win over Philadelphia in the NL championship series, San Francisco has outscored Texas 20-7 and outhit the Rangers .314 to .227.
C.J. Wilson allowed Renteria's fifth-inning homer, then left the mound accompanied by a trainer with a blister on the middle finger of his pitching hand following a leadoff walk in the seventh. Juan Uribe added a run-scoring single against reliever Darren Oliver.
San Francisco pulled away as Rangers manager Ron Washington again made bullpen moves too late. Derek Holland relieved with a man on and forced in a run with three straight walks, the last to Aubrey Huff, and Mark Lowe forced in another run with a walk to Uribe.
Renteria, whose 11th-inning single won Game 7 of the 1997 Series for Florida against Cleveland, followed with a two-run single to left. Pinch-hitter Aaron Rowand hit a two-run triple against Michael Kirkman, and Andres Torres doubled in a run.
Cain allowed four hits in 7 2-3 innings, struck out two and walked two - one intentional. With the Giants ahead 2-0, left-handed specialist Javier Lopez retired Josh Hamilton on a lazy flyout to strand a runner on second in the eighth.
As fans stood cheering, Guillermo Mota completed the four-hitter.
Forty of the previous 51 teams to take a 2-0 lead have gone on to win the title, including seven straight and 13 of the last 14. The last to overcome a 2-0 deficit was the 1996 New York Yankees against Atlanta. The Giants have won each time they took a 2-0 lead: in 1922, 1933 and 1954.
San Francisco improved to 11-0 against Texas at AT&T Park and got its third shutout in nine postseason wins. The Giants sent the high-octane Rangers offense to its first shutout since Sept. 23.
But after a day off, the Series resumes for the first time in Arlington, Texas. Colby Lewis starts Game 3 for the Rangers on Saturday night against Jonathan Sanchez.
Much of the pitching buzz coming into the Series was over Texas' Cliff Lee, who had been unbeaten in postseason play before getting hit hard Wednesday.
Cain has been even sharper, pitching 21 1-3 innings in three postseason starts without allowing any earned runs. Sparkling but not surprising, given the Giants led the major leagues in ERA during the regular season.
Cain credited rookie catcher Buster Posey.
"I think it's a little bit of everything," Cain said. "Buster's doing a great job of putting down the right fingers. He's been calling the right pitches."
Cain pitched out of trouble a few times against Texas, which went 0 for 9 with runners in scoring position.
Ian Kinsler's drive on an 0-2 pitch leading off the fifth hit flush off the top of the fence, just to the left of the 399-foot sign in center field, bounded up and was caught by Torres, who held him to a double. At first it was unclear whether the ball had gone over the wall, but relays showed umpires got the call correct.
Kinsler was stranded when David Murphy lined to shortstop, Matt Treanor grounded to shortstop and - following an intentional walk - Wilson grounded weakly to first.
Renteria led off the bottom half by pulling an 0-1 pitch at the letters down the left-field line, where it landed about eight rows deep, next to an alleyway. Renteria had gone 53 straight at-bats without a home run since connecting off the Los Angeles Dodgers' Ted Lilly on Sept. 4 and had not homered at AT&T Park since July 27 against Florida's Brian Sanches.
One-out singles by Michael Young and Hamilton followed by a wild pitch put runners at second and third in the sixth. But Nelson Cruz fouled out to first and Kinsler popped out to short right.
Washington made a few changes after a sloppy defeat in the opener. He benched Vladimir Guerrero, who made two errors in right field. Cruz shifted to his regular spot in right, with Murphy replacing Cruz in left. Treanor took over from Bengie Molina behind the plate.
Elvis Andrus and Cruz failed to get hits, stopping their 12-game postseason hitting streak.
NOTES: Former 49ers QB Joe Montana was at the game and was shown on the videboard, as was Journey's Steve Perry... The ceremonial first pitch was thrown out by Megan Armstrong and Nancy Mitchell, daughters of Bobby Thomson, who died in August. Thomson's Shot Heard Round the World won the 1951 NL pennant for the New York Giants over the Brooklyn Dodgers. ... Texas hadn't forced in two runs in an inning with bases-loaded walks since Rich Harden did it on April 7 against Toronto, according to STATS LLC.