Make it five such victories for the reigning World Series champions by early May.
Torres lined a game-ending single to right field with two outs in the 10th inning to score Posey for the winning run, lifting the Giants to a 4-3 victory against the Philadelphia Phillies on Wednesday to avoid a sweep.
"I think we've got a group of guys that's going to continue to scrap and go out there and put pressure on the other team," Posey said.
"We've got a lot of guys who have been here a few years and we've played a lot of tight games the last three years. The more you do it, the more, I don't want to say comfortable, but I think you gain more confidence when you're in that situation more often."
Posey hit a pinch-hit single to start the 10th against Antonio Bastardo (1-1) and was sacrificed to second by Joaquin Arias. Posey advanced to third on a wild pitch before Torres came through with his fourth career game-ending hit.
Manager Bruce Bochy praised Posey's base running with the game on the line.
"More than anything, at that point in the game, I thought it was worth the chance to take that risk," Posey said of running for third. "You see it and go."
Zito pitched another gem in his home ballpark and Hunter Pence homered against his former club for the second time during the three-game series, but Romo wasn't his usual spot-on self in the ninth.
Pence sent a 2-2 pitch into the stands in left field leading off the second for his seventh homer. Marco Scutaro hit a go-ahead single in the fifth to score Gregor Blanco after he singled and stole second.
Still, Zito is 3-0 with a 0.55 ERA in his four home starts this season -- and the home ERA ranked third-lowest in the majors. And San Francisco has won Zito's past 11 regular-season starts in the waterfront ballpark.
"We obviously don't want to be playing down to the wire," Zito said. "We'd like to go out there and boat-race teams, but unfortunately it's the big leagues and that doesn't happen too often."
He pitched into the eighth, struck out three and didn't walk a batter for the first time this season.
Zito left to a rousing standing ovation from the sellout crowd of 41,048 in the eighth and added an RBI single in the sixth.
Coming off a pair of no-decisions against the division rival Padres and Dodgers, Zito helped get the Giants back on track following a pair of 6-2 losses on the heels of their season-best six-game winning streak.
Santiago Casilla took over from Zito after Carlos Ruiz's leadoff single, but he came out with a right knee injury two batters later and Jeremy Affeldt finished the eighth. Romo allowed Jimmy Rollins' leadoff double, an RBI single to Chase Utley and Delmon Young's tying sacrifice fly in the top of the ninth.
Kevin Frandsen hit his first home run of the year against his former team to tie the game leading off the fourth. He was booed as he rounded the bases. That was just the second earned run allowed by Zito in 33 innings at home this season.
Philadelphia did little else until late, and couldn't pull off the club's first three-game series sweep in San Francisco since May 18-20, 1984. The Phillies have never swept at 14-year-old AT&T Park.
Their 69-year-old skipper, Charlie Manuel, managed his 1,331st game for the franchise, matching Gene Mauch for the most in team history.
"We have core guys on this team who know to win. We'll survive," Manuel said. "Others can think what they want, it's what we believe."
The Phillies lost for the first time in four career starts by Jonathan Pettibone, who threw 112 pitches over 5 2/3 innings.
Rollins doubled with one out in the sixth, but was thrown out at third for his second caught stealing in four attempts.
Zito's single in the sixth chased Philadelphia's rookie right-hander. With two outs, Pettibone intentionally walked Guillermo Quiroz to get to Zito, who singled to right for his fourth hit of the season and second RBI.
The Phillies received the news right-hander Roy Halladay would have arthroscopic shoulder surgery but could still return this year if all goes well.
The team travels to the Arizona desert to continue a seven-game road trip that has shown some positive signs after Philadelphia dropped the final two games of its homestand -- including a 14-2 defeat to the Marlins on Sunday.
"These wins are fine, but it doesn't matter right now," slugger Ryan Howard said. "As long as we get hot at the right time."
An MRI on Giants center fielder Angel Pagan's right leg revealed a strained groin rather than a hamstring injury, which caused him to miss games Sunday and Monday before he returned Tuesday. He was held out of the lineup Wednesday as a precaution.
Casilla was to have an MRI exam later Wednesday or Thursday. ... Posey had the day off after a night game until his pinch-hit appearance in the 10th. ... The Phillies will call up RHP Tyler Cloyd from Triple-A Lehigh Valley to take Halladay's turn in the rotation Friday at Arizona.