Two of the top left-handed pitchers in the National League square off Friday when the San Francisco Giants begin a three-game series against the visiting Philadelphia Phillies. Philadelphia's Cole Hamels owns a 1.76 ERA over his last 18 starts, while the San Francisco's Madison Bumgarner has allowed three earned runs over his last 17 innings. The Giants, who snapped a five-game losing skid with a 7-1 win over the Chicago White Sox on Wednesday, reside 5 1/2 games behind the first-place Los Angeles Dodgers in the NL West.San Francisco has lost 13 of its last 19 contests and will be without Brandon Belt for the entire series while the first baseman deals with post-concussion syndrome. Belt missed 12 games last month after suffering a concussion on July 19, and he returned to the seven-day disabled list last Friday after experiencing recurring symptoms. Philadelphia has lost five of its last six, but rookie reliever Ken Giles has been a bright spot with a 1.44 ERA and 37 strikeouts over his first 25 innings.TV: 10:15 p.m. ET, CSN (Philadelphia), NBC Bay Area (San Francisco)PITCHING MATCHUP: Phillies LH Cole Hamels (6-6, 2.37 ERA) vs. Giants LH Madison Bumgarner (13-9, 3.22)Hamels enters Friday's contest as one of the hottest pitchers in the majors with a 0.73 ERA over his last five starts. The San Diego native, who is 6-3 with a 3.53 ERA in 13 career starts against San Francisco, has thrown seven or more innings while allowing one or fewer runs in five consecutive starts. "He's on a terrific run," manager Ryne Sandberg told reporters. "He definitely gives us a chance to win every time he goes out there."Bumgarner has tossed complete games in each of his last two starts, including last Friday when he threw a season-high 123 pitches against Kansas City. The two-time All-Star is 2-2 with a 2.89 ERA in four career starts versus Philadelphia, including eight scoreless innings on July 23. Ben Revere has four hits in five at-bats against Bumgarner, who has struggled at AT&T Park this season with a 4-6 mark and 5.60 ERA in 11 starts.WALK-OFFS1. San Francisco CF Angel Pagan is 11-for-36 during his eight-game hitting streak.2. The Phillies have lost 39 of their last 45 games when scoring three runs or fewer.3. The Giants have hit a total of two home runs in their past nine games.PREDICTION: Phillies 3, Giants 1