PITTSBURGH -- For the second straight game, the Pirates had a solid pathway to a win, getting a quality start from a rookie starter and a grand slam on offense.

And again, they lost, this time squandering six strong innings from No. 2 overall prospect Paul Skenes with another bullpen collapse, dropping the rubber match to the Giants, 7-6, at PNC Park on Thursday afternoon.

Skenes did not have his best breaking stuff and relied on his four-seamer and splinker -- his splitter-sinker hybrid that gets classified as a splitter -- for most of his afternoon. While San Francisco was able to pick up six singles, it couldn’t string much together, thanks in part to a couple of double plays.

One of those double plays was with the splinker, the pitch Skenes had working the best, especially early. He got six whiffs with the pitch, as well as six groundouts on the eight batted balls the Giants put in play against it.

“That’s kind of the M.O. of that pitch,” said Skenes. “It’s going to get ground balls, weak contact, so I was happy with it.”

Skenes did not have quite the dizzying stuff that he showed in his last outing at Wrigley Field. His fastball velocity maxed out at only 100.3 mph, and he only hit 100 mph four times. He had just three strikeouts and 13 whiffs. But even not quite at 100 percent, Skenes is tough to square up.

“Obviously, it wasn't his best, you know what I mean?” said catcher Joey Bart. “But if you can go out there and put that kind of performance on without your best stuff, then there's definitely something to build on.”

“Just gotta get back to what makes me good and trusting my stuff,” Skenes said about moving forward. “You’ll take your singles, but the odds of them getting four singles in a row, I trust myself over pretty much any lineup. It’s just playing the odds a little bit.”

Have we seen better from Skenes? Sure. Can anyone find much fault with six innings pitched and just one run allowed? Probably not.

“I wish it were a little bit more,” Skenes said. “Had a couple long innings, but there’s going to be those games. I thought I made do and put the team in the best position to win.”

In retrospect, the Pirates probably wished Skenes could have gone a little deeper into the game, too, even though that was impractical after he had already thrown 93 pitches (62 strikes).

Thanks to a grand slam by Bart and solo shots by Andrew McCutchen and Bryan Reynolds, the Pirates built up a 5-1 lead after six innings and a 6-2 lead after seven. Still shorthanded after heavy bullpen usage the past two days, they turned to the recently recalled Jose Hernandez in the seventh, where he allowed one home run and nearly a second. Hunter Stratton had to finish that frame and was asked to continue on in the eighth, where he was charged with five runs, though the last one was a product of Aroldis Chapman throwing a wild pitch and then surrendering the deciding base hit on an 0-2 count to Brett Wisely after a passed ball by Bart.

“The guy [Skenes] comes out of the game, and they’re a little limited down there,” said Giants manager Bob Melvin. “We put together some really good at-bats, and we were tenacious really until the last out.”

While the past two nights have been the most blatant examples of the bullpen’s struggles this season, the month of May has been particularly rough for them, with 45 runs (39 earned) allowed over 62 innings. That 5.66 ERA is the worst in the National League this month, and what was supposed to be a strength has been a weakness for this club.

“It's a concern,” Pirates manager Derek Shelton said. “Our bullpen's got to be better. We have, what, a 5-1 lead yesterday? 6-2 lead today? We have to be better. Our bullpen has to be better. We have to win games like that.”

With Skenes, Jared Jones and Mitch Keller, Pittsburgh has set itself up nicely to have a formidable top of the rotation for years to come. But they can’t do it all on the pitching side.

“Frustrating,” Shelton said. “Very frustrating. We have to finish games like that.”