PITTSBURGH -- The Padres finished a frustrating first half of the season with another frustrating loss.

San Diego built a four-run lead by the fourth inning on Thursday afternoon, but wound up taking a 5-4 loss to the Pirates at PNC Park. The Padres were swept in the three-game series and saw their losing streak extend to five games. They’ve dropped eight of their past 10.

The Pirates had lost 12 of their previous 13 games prior to the series.

At the midway point of the season, the Padres have a 37-44 record. That was not how they envisioned this year going after reaching the NLCS last season and entering 2023 aiming to dethrone the Dodgers and win the NL West for the first time since 2006.

Right-hander Joe Musgrove grew up a Padres fan in El Cajon, Calif., and understands the frustration both inside and outside the clubhouse. But he also believes the Padres are ready for a second-half surge.

Musgrove turned in a quality start, allowing two runs in six innings, but the Pirates scored three runs (two earned) off reliever Tim Hill (1-2) in the seventh to go ahead 5-4.

“It’s really bad right now,” Musgrove said. “I know from the outside it looks like a lot of overpaid guys who aren’t performing well. Sometimes, there’s no answer. It’s been a tough first half of the season, and we feel it.

“But if you think this team is rolling over, you’re sorely mistaken. We’re trying to find out what it is. We’re switching up routines, having meetings, talking about all these things, but it’s just not going our way right now. It feels like every loss that goes by piles on and piles on and piles on.

“We need to put a couple of good games together and go on a little bit of a run,” Musgrove continued. “There’s plenty of fight left in this team, and we haven’t played our best ball yet.”

Padres manager Bob Melvin was asked if he could have envisioned on Opening Day that his team would be seven games under .500 at the halfway point of the season.

“I don’t think anybody could,” he said. “We’ve been asked that a lot.”

It is indeed a constant topic of conversation around the Padres. However, like Musgrove, Melvin believes his team can put together a second-half surge.

“Look, we have to put these [games] away and be mentally tough,” he said. “We’ve got to, at some point in time, start over and understand this isn’t what we wanted, and there’s nothing we can do about it now but have a big second half.”

Things started off well enough for the Padres, as they rallied for three runs in the second inning to open the scoring. Ha-Seong Kim hit a sacrifice fly and Trent Grisham followed with a two-run homer to right.

Kim added a solo shot in the fourth to stretch the Padres’ lead to 4-0, connecting on a 97.3 mph fastball from Luis L. Ortiz.

That is the fastest pitch against which Kim has homered in his three seasons since coming to the Padres from the Korea Baseball Organization. His other eight career hits on faster pitches were all singles.

Before Sunday, Kim had hit only one home run on a 97 mph pitch, coming off the Rockies’ Antonio Santos on Aug. 1, 2021. However, Kim now has two in the last four games, as he turned around a 97 mph heater from the Nationals’ Jordan Weems on Sunday at Petco Park.

But it wasn’t enough to end the Padres’ skid after the Pirates scored the game’s final five runs. Pittsburgh’s three-run seventh was keyed by an error on Hill, who threw wildly to first base on Jack Suwinski’s infield single after initial indecision as to whether to try for the putout or let the ball roll and hope it went foul.

Two runs scored on the play. One out later, Henry Davis hit a go-ahead single off Luis García.

“I’ve said all year we probably haven’t gotten our timing right,” Melvin said. “We scored some runs early and [Musgrove] does a nice job. Obviously when you make an error late in the game, it costs you, though.”