Manager Dale Sveum is quickly tiring of the mental mistakes that are costing the Chicago Cubs in close games.

This time, in the team's 11th straight road loss, the culprit was shortstop Starlin Castro.

The Cubs missed chances against Ryan Vogelsong and lost 3-2 Monday to get swept by the San Francisco Giants, dropping the four games by a combined five total runs.

Leading by one with the bases loaded and one out in the fifth, Cubs starter Jeff Samardzija induced a groundball by Brandon Crawford. Second baseman Darwin Barney flipped the ball to shortstop Castro at second, but he didn't attempt a throw to first and instead began trotting toward the dugout believing the inning was over.

"That kind of thing can't happen because it's very embarrassing for me, my teammates, the manager, everybody," Castro said.

The Giants tied it on that play.

"It's something that's obviously unacceptable at any time," Sveum said. "Whether we could have turned the double play or not is irrelevant to not knowing how many outs there are in the most important part of the game. These things have got to stop happening or he's going to stop playing. These kind of things are things that my son does in high school maybe."

Vogelsong won his fourth straight decision after Buster Posey scored the go-ahead run on a double-play groundball by Joaquin Arias in the seventh inning.

San Francisco's starters have gone seven straight games pitching seven or more innings while allowing two or fewer runs, just the second time it has been done since the franchise came West in 1958. Giants pitchers accomplished the feat in nine consecutive games from July 1-10, 1988, according to STATS LLC.

In this series, Madison Bumgarner, Matt Cain and Barry Zito had won before Vogelsong's impressive performance on a rare wraparound getaway game on a Monday.

"You don't want to be the weak link," Vogelsong said. "Three games like that, I don't want to be the guy who doesn't come through. It's a tough act to follow those three guys, those three outings."

Crawford hit an RBI double and drove in another run on a fielder's choice to back Vogelsong (4-2), helping the Giants to their season-best fourth straight victory.

San Francisco (31-24) moved a season-best seven games over .500. The Giants began the day trailing NL West-leading Los Angeles by three games. The Dodgers had a night game at Philadelphia.

Cubs reliever Carlos Marmol (0-2) was hit with a line drive on Angel Pagan's infield single in the seventh but stayed in the game after being checked out, then walked Brandon Belt on four pitches to load the bases for Arias.

Pagan singled in the fifth for a 28-game home hitting streak, the longest in franchise history since 1900. He tipped his batting helmet and clapped his hands at first base in appreciation following a warm ovation from the sellout crowd of 41,524 on a day that began with sporadic rain in the early innings after the tarp came off late morning.

The Giants completed the club's first sweep of the season in its fifth try — the games decided by five total runs. San Francisco pulled off its first four-game sweep of Chicago since June 17-20, 1999, at Candlestick Park.

"Pitching was just outstanding," Giants manager Bruce Bochy said. "We scratched and clawed for the runs we got. These games could have gone either way."

Samardzija matched his season high with five walks while striking out six in five innings. The right-hander allowed seven hits and two runs but has only one win in his last five outings.

"Their whole lineup made me work," he said. "I need to be in the zone early in the count. It's kind of a broken record when I have outings like this."

Pinch-hitter Adrian Cardenas hit a one-out double for Chicago in the seventh for his fifth major league hit — all of them doubles — but the Cubs couldn't avoid an 11th straight loss away from Wrigley Field. It's their longest road skid since the 1954 team lost 11 in a row from June 18-29.

Chicago also lost a one-run game for the 10th straight time.

Vogelsong allowed four straight singles and five total in the second, including consecutive run-scoring hits by Steve Clevenger and Samardzija. After leadoff man Tony Campana's single, Vogelsong received a mound visit from pitching coach Dave Righetti before fielding Castro's grounder and throwing him out on a close play at first.

Vogelsong pitched seven innings and didn't walk a batter for the first time this season. Jeremy Affeldt recorded the final six outs for his first save in his first chance, getting a leaping catch from second baseman Ryan Theriot on Clevenger's high liner to end it.

"That was definitely the best all-around stuff I've had," Vogelsong said.