PITTSBURGH -- An old baseball adage is that good pitching tops even good hitting. Right now, the New York Mets' bad hitting is struggling against any and all pitching.

Juan Nicasio limited the Mets to one run over five innings, backup catcher Chris Stewart had two key hits and the Pittsburgh Pirates completed a doubleheader sweep of New York, winning the second game 3-1 on Tuesday night.

The Pirates had lost five of six before taking the opener, also 3-1, as left-hander Jonathon Niese gave up four hits over seven shutout innings in his first start against the team that traded him last winter. Jordy Mercer hit his first homer in PNC Park in 22 months.

Mets left-hander Steven Matz (7-2) had lost only once previously in the majors before dropping the first game, while Mets right-hander Jacob deGrom (3-2) had lost only once this season before giving up three runs over six innings in the second.

The Pirates have won nine in a row over the Mets dating to the 2014 season, including eight over the past two seasons. Pittsburgh's doubleheader sweep was its first over the Mets since Sept. 19, 2004 -- or the last twinbill between the two.

Again, the Mets labored for runs -- they've scored only one each while losing their last three games, and they've dropped five of seven overall.

"We've got some guys struggling," Mets manager Terry Collins said.

What's curious is the Mets are near of the top of the NL with 77 homers but near the bottom in batting average. No team has led a league in homers but finished last in batting since the 1915 Phillies, according to Elias.

"That's a team that's got power, but we were able to make pitches," Pirates manager Clint Hurdle said. "We had just a couple of situations where we had runners in scoring position that we had to work through. A really, really good job on the mound all day."

Nicasio (5-4) followed Niese's effective start in the first game by striking out seven, walking two and yielding only three hits over five-plus innings, the first time in five starts he's given up fewer than three earned runs.

Mark Melancon worked the ninth for his 19th save in 20 chances and second of the day after Neftali Feliz, Tony Watson and Jared Hughes each pitched a scoreless relief inning, with the five Pirates pitchers combining for 14 strikeouts. Feliz and Melancon pitched in both games.

"I did everything I do normally -- and just came out and competed," Feliz said.

The Mets did what they've been doing, too.

"I don't know if there's one thing causing it. Obviously, one thing we have not really been applying some of the stuff we're working on," Collins said. "We're striking out too much. We need to make better contact."

DeGrom struck out nine and didn't walk any, but was hurt by a makeshift bottom of the Pirates lineup in which the bottom four hitters, including Nicasio, had five hits, scored three runs and drove in two.

"When you go there, you don't think about that (the struggling offense)," deGrom said. "Everybody on this staff just goes out there trying to put up zeroes. Everyone is grinding right now and it's a tough stretch. It can turn around tomorrow because it's a funny game."

DeGrom allowed one earned run or fewer in five of his first nine starts, but the Pirates got to him for two runs in the second. Mercer singled with one out, Sean Rodriguez doubled, Cole Figueroa drove in Mercer with a ground out and No. 8 hitter Stewart singled for his fifth RBI of the season.

Nicasio retired the first 12 batters in order before Neil Walker got the Mets' first hit, a single leading off the fifth. He was erased on a double play, but Michael Conforto's two-out double and a Nicasio wild pitch put him in position to score on No. 8 hitter Kevin Plawecki's RBI single.

"A strong outing for the 90 pitches he was out there," Hurdle said of Nicasio.

The Pirates got that run back in their half of the fifth on John Jaso's run-scoring double that followed Stewart's second single and Nicasio's single that deflected off deGrom and into left field against a drawn-in infield. Nicasio had been 2-for-16.

Nicasio gave up 15 earned runs in 20 innings while going 1-2 in his four May starts.

NOTES: Mets 2B Neil Walker received a lengthy ovation from the fans before his initial at-bat in the first game, in his return to the hometown where he played for six seasons. ... Pirates SS Jordy Mercer's home run in the opener was his first at PNC Park since Aug. 31, 2014. ... Former Mets LHP Jonathon Niese induced his former teammates into grounding into 14 ground ball outs in the first game. ... Mets OF Curtis Granderson was 2-for-53 (.038) during his Mets career against Pittsburgh until he homered in the eighth off RHP Neftali Feliz. ... RHP Jameson Taillon, the Pirates' top pitching prospect, is being called up from Triple-A Indianapolis to make his major league debut Wednesday against the New York Mets. He will face RHP Noah Syndergaard (6-2). ... Pirates LHP Francisco Liriano (4-5) was scheduled to start against the Mets, but was bumped back to Saturday to face the Cardinals. ... Because of the Monday rainout, Mets RHP Logan Verrett (3-3) will start Saturday in Milwaukee. ..... The Pirates called up RHP Wilfredo Boscan to be their 26th man in the second game of the doubleheader. The Mets added INF Eric Campbell.