Chicago Cubs' Starlin Castro watches his game-winning double against the San Francisco Giants during the ninth inning.
Sergio Romo proved he wasn't perfect.
The Giants' closer entered Friday's game against the Chicago Cubs six for six in save chances this season.
But after a ninth-inning San Francisco comeback, he could not hold a 3-2 lead as Starlin Castro's two-out double off the center-field wall gave the Cubs a 4-3 victory.
Chicago led 2-0 heading into the top of the ninth, but closer Kyuji Fujikawa allowed a one-out RBI single by Pablo Sandoval and hit Buster Posey with a pitch before Brandon Belt's two-out double down the right-field line scored two runs and gave the Giants a 3-2 lead.
Romo was then summoned from the bullpen for his fourth appearance in five days.
Pinch-hitter Dioner Navarro tied the game with a home run to right field to lead off the inning, the first pinch-hit homer of the season for the Cubs.
"I made a good pitch. He put the ball in play," Romo said. "Things happen when you put the ball in play. You tip the cap to him. No excuses."
Romo then struck out Luis Valbuena and Brent Lillibridge before David DeJesus singled to center to set up Castro's winner.
"It's a great comeback and a tough loss to go with it," Giants manager Bruce Bochy said. "The boys battled back hard there in the ninth. Sergio's been so good, he just got a couple balls up in the ninth.
"It's going to happen and he's going to have to deal with the occasional hiccup. That's the life of a closer."
Matt Cain made his first start since giving up nine earned runs in 3 2-3 innings in a 14-3 loss to St. Louis on April 7. The Giants' ace allowed seven hits— solo home runs to DeJesus and Castro while striking out six and walking two.
"A lot of time if you make good pitches, you get rewarded for it," Cain said. "If you make bad pitches, guys get the ball up in the air and if the wind's blowing the wrong way, you're at the mercy of whatever's going to happen."
Carlos Villanueva pitched 7 1-3 shutout innings and allowed three hits and struck out three.
The strong start was Villanueva's second in a row. Villanueva made his Cubs debut April 6 at Atlanta and allowed one run in 6 2-3 innings.
After allowing Angel Pagan to lead off the game with a single, Villanueva retired the next 12 batters until Hunter Pence singled with one out in the fifth.
Villanueva was replaced with one out in the eighth by James Russell after giving up a single to Gregor Blanco. Brandon Crawford singled off Russell, but the Cubs' left-hander got pinch-hitter Andres Torres to ground into a 5-4-3 double play.
Chicago took a 1-0 lead in the bottom of the third when DeJesus led off with his home run. DeJesus' blast was helped by a wind that was blowing out to right field. DeJesus had three hits.
The Cubs doubled their lead in the bottom of the fifth when Castro homered, taking a 1-2 pitch from Cain and lining it into the left-field bleachers.
San Francisco threatened in the sixth after Crawford led off with a walk and was sacrificed to second by Cain. With two outs, Scutaro's sharp grounder to third was snagged by Steve Clevenger, who threw to first to get the San Francisco second baseman.
Sandoval's ninth-inning RBI single extended his hitting streak to six games.