PITTSBURGH -- Before this series, the last time the Pirates and Mariners met was July 27, 2016. It may not seem like that long ago, but consider this: That night at PNC Park, Gerrit Cole started opposite James Paxton. And only one player from each team’s starting lineup in that game still plays for that team: Seattle’s Kyle Seager and Pittsburgh’s Starling Marte.

Combine a lack of familiarity with a dearth of recent history and a pair of expanded rosters, and it’s no wonder why Pirates manager Clint Hurdle called this series “one of the biggest Interleague challenges we’ve had in the nine years that I’ve been here.”

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Preparation and information weren’t a problem, Hurdle said Wednesday afternoon, crediting Pirates advance scout Jim Dedrick for his diligent work. But execution was an issue once again in the Bucs’ 4-1 loss to the Mariners on Wednesday night before a crowd of 9,875 at PNC Park.

The Pirates have lost five straight games, and they’ve been outscored by 41 runs (57-16) during that stretch against the Cubs and Mariners. Wednesday’s defeat dropped the Pirates to 21-42 in the second half.

Pitching was clearly the culprit last weekend at Wrigley Field, where the Pirates set a handful of ignominious records while being swept by the Cubs. Their starting pitching was better on Tuesday, when Mitch Keller allowed only two runs in five innings, and their bullpen backed up starter Dario Agrazal with four scoreless innings on Wednesday.

Agrazal gave up four runs in five innings, which he completed with a reasonable 74 pitches, but his struggles were condensed into two sequences. One of them reinforced the idea that the Pirates’ issues the past two nights are rooted in poor execution, not a lack of familiarity.

With two on and two outs in the second inning, Agrazal threw a low changeup to Mariners No. 8 hitter Dylan Moore -- who, Hurdle noted, was in the scouting report as a low-ball hitter -- and Moore hit it to left for a two-run double.

“That one hurt,” Hurdle said.

In the fourth, Kyle Lewis and Tom Murphy launched back-to-back homers against sinkers from Agrazal. Just like that, the Pirates were in a four-run hole.

If there was a positive to glean from Agrazal’s outing, it’s that he struck out six and walked only one. The rookie right-hander entered the night averaging only 4.3 strikeouts per nine innings in the Majors. He made the Mariners swing and miss on five of his 13 sliders, a pitch he focused on in the week since his last start.

“These past seven days, I’ve been working very diligently on my breaking balls -- the movement, location, execution,” Agrazal said through interpreter Mike Gonzalez. “I saw some of the fruit of it this evening.”

It went unrewarded, however, as the Bucs’ bats have gone quiet -- which is perhaps not a surprise when they’re playing without their Nos. 3 and 4 hitters, Starling Marte and Josh Bell. During this five-game losing streak, the Pirates have given up 19 homers and hit none.

Left-hander Marco Gonzales shut out Pittsburgh for seven innings in the series opener, and Seattle did it by committee on Wednesday, with Justin Dunn (two innings), Tommy Milone (five), Anthony Bass and Matt Magill combining to allow only six hits and three walks despite recording only two strikeouts as a staff.

The Pirates produced nine hard-hit balls, according to Statcast, but seven of them resulted in outs while only two fell for hits. Meanwhile, six of their outs were hit to either the pitcher or catcher.

The Bucs’ only run on Wednesday came in the eighth, when Cole Tucker knocked a pinch-hit triple to right and scored on Kevin Newman’s groundout. They made better contact after putting two men on in the ninth, but Mariners center fielder Braden Bishop made a pair of nice plays to snag Adam Frazier’s 96 mph flyball and a 108.5 mph line drive off the bat of Elias Díaz.

“The change of speeds absolutely negated any hard contact. Once Milone got out, we took some better swings. We hit some balls hard, but it was too late,” Hurdle said. “We hit balls hard. We didn’t get them to where the grass was. They found gloves.”