PITTSBURGH -- An explosive third inning propelled the San Francisco Giants to a 5-3 win against the Pittsburgh Pirates at PNC Park on Thursday.

Giants second baseman Joe Panik earned three RBIs on a bases-clearing triple in the third. Right fielder Mac Williamson added two RBI of his own, one in the third and another coming on his second career home run two innings later.

San Francisco (47-27) took three of four in Pittsburgh before heading home for a three-game weekend series against the Philadelphia Phillies starting Friday. The Giants have won 11 of their past 12 games.

The Pirates (34-39) continued their steep slide with a 20th loss in 26 games since winning five straight from May 23-27. They will face the Los Angeles Dodgers at PNC Park on Friday.

Pirates left-hander Jon Niese, who lost a third consecutive decision, cruised with a 1-0 lead early. Then the third inning came.

After retiring each of the Giants' first six batters without allowing a ball out of the infield, Niese was battered for four runs in the top of the third. Giants left fielder Jarrett Parker walked before third baseman Conor Gillaspie singled to center and rookie right-hander Albert Suarez's sacrifice bunt moved them up a base.

Center fielder Denard Span forced another walk to load the bases then Panik hit his triple past Pirates center fielder Gregory Polanco, who overran the ball. Williamson, who would later belt Niese's two-seam fastball 446 feet to left-center field and give the Giants a 5-3 lead in the sixth inning, smacked a single over third baseman Jung Ho Kang's glove to extend San Francisco's lead to 4-1 in the third.

Niese's struggles came and went, while Suarez battled through spotty control.

The rookie improved to 3-1 by limited the Pirates to three runs, two earned, on four hits with six strikeouts and two walks in five innings pitched.

Suarez surrendered a run without allowing a hit in the first inning. After hitting first baseman John Jaso, the first batter he faced, and forcing Josh Harrison into a fielder's choice, Suarez threw the ball away on an errant pickoff attempt.

Harrison moved from first base to third before Polanco drove him in with a sacrifice fly to center.

The Pirates had runners on the corners with no outs in the second inning, but failed to build upon their 1-0 cushion. Suarez struck out the side to preserve the Giants' one-run deficit before San Francisco's breakout third inning.

Pittsburgh got two runs back when Suarez continued to struggle in the third. Jaso singled to right before Harrison belted a triple to left-center field. Polanco scored Harrison from third with a sacrifice fly for the second time in three innings to cut San Francisco's lead to 4-3.

Suarez seemed to gain some control the following inning, but surrendered a two-out double to Niese, who entered Thursday batting .083. He responded by striking out Jaso.

After Niese's double, Pittsburgh didn't record another hit until left fielder Sean Rodriguez singled with two outs in the ninth.

NOTES: The Giants made several lineup changes the day after their 7-6 come-from-behind win against the Pirates on Wednesday. Buster Posey moved to first base from catcher, where Trevor Brown started Thursday. ... Giants OF Mac Williamson hit third, replacing 1B Brandon Belt, who went 1-for-5 with two strikeouts Wednesday. ... CF Denard Span played a third consecutive game since returning from a stiff neck on Tuesday. Span had five hits in 11 at bats over his previous two games. ... Pirates OFs Andrew McCutchen and Starling Marte were each left out of the starting lineup. McCutchen entered Thursday batting .238 after reaching safely once in his previous 10 at bats. ... Marte, who is battling a sore left foot, pinch-hit for C Chris Stewart in the eighth inning Wednesday. Pirates manager Clint Hurdle said Marte would have been replaced by a pinch runner if he reached base. ... C Erik Kratz started in place of Stewart, who returned from a knee injury Tuesday.