Based on the difficulty they had sweeping baseball's worst team, the NL West-leading Giants are unlikely to overlook Chicago in Friday's opener -- especially after the resilience the Cubs displayed in their last gameSan Francisco (74-57) arrives in Chicago with a season-high 4 1/2-game lead over Los Angeles in the division after beating Houston 8-4 on Thursday. Nothing came easy against the Astros for the Giants, who rallied in the ninth in the opener, nearly coughed up a four-run lead in the middle game and overcame a 4-0 deficit in the finale."We kept the energy up just enough to get three wins," said Brandon Belt, who went 4 for 5 with two doubles and an RBI on Thursday, "and hopefully we can keep it going."The Giants also had trouble putting away the Cubs, owner of the majors' second-worst record, in early June at AT&T Park, though they managed to win all four games. San Francisco outscored Chicago 11-6, winning three times by one run.Madison Bumgarner (14-8, 2.93 ERA) set the tone for that series, allowing two runs while striking out 11 in eight innings of a 4-3 win on June 1. He is 3-1 with a 1.55 ERA and 37 strikeouts in 29 innings in his last four starts against the Cubs (50-80).Bumgarner takes the ball after allowing four runs, seven hits and a season-high tying four walks in 6 1/3 innings of Saturday's 7-3 loss to Atlanta. The left-hander had a 1.93 ERA in his previous eight starts."It happens throughout the course of a season that you get out of whack," Bumgarner said. "That was the first time all season I wasn't able to get it back."Although he hasn't had much trouble against Chicago, he'll have to be careful facing Starlin Castro, who is 7 for 16 against Bumgarner -- his best average against any pitcher he's faced that many times.The Cubs have lost 22 of 29, but enter this series in good spirits after rallying to beat Milwaukee 12-11 on Thursday to salvage the finale of a four-game series. Chicago trailed by six and capped a three-run ninth inning with Alfonso Soriano's one-out RBI single.The Cubs, who had averaged 2.9 runs in their previous eight games, finished with eight extra-base hits and a season-high 11 walks, and hope this outburst is a sign of things to come."I think it will help the offense and the clubhouse because we came back," Soriano told the Cubs' official website. "It was a big game for us to win that game."Chris Volstad (1-9, 6.28) is also hoping he can build on his latest outing.Volstad allowed three hits and three walks in 6 2/3 innings of Sunday's 5-0 win over Colorado, snapping a 24-start winless streak for his first victory since helping Florida beat Houston on July 10, 2011.This will be the right-hander's first outing of the season versus the Giants, against whom he is 1-2 with a 2.67 ERA in four career starts.Angel Pagan, San Francisco's hottest hitter with a .393 average in his last 13 games, is 1 for 13 lifetime against Volstad.Hunter Pence has also been locked in, batting .467 with five RBIs in his last four games, and is 7 for 18 lifetime against Volstad.