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The Pittsburgh Pirates were right on the NL Central leaders' tail earlier this month and held a comfortable lead for the league's second wild-card spot.

Now their postseason grip is gone -- and they're on the verge of being closer to the fourth-place Milwaukee Brewers than first.

Another loss Saturday night would match the Pirates' longest skid of 2012 at five, while the visiting Brewers hope the return of right-hander Shaun Marcum can help them win a season-high fifth straight game.

Pittsburgh (67-58) led the Central at the All-Star break and was only 2 1/2 games behind Cincinnati as recently as Aug. 8 while holding a 3 1/2-game lead on St. Louis for the NL's second wild-card berth.

Just 17 days later the Pirates are in third place, two games behind the Cardinals for that final playoff spot. Friday's 6-5 loss to Milwaukee kept them eight back of the Reds, and with another loss Saturday they'll match their five-game skid from April 10-14 and be closer to the Brewers (58-66) than the division leaders.

Friday's loss nearly turned much worse. Andrew McCutchen slammed his left knee into the outfield wall trying to make a catch in the seventh inning but remained in the game.

"When you're not playing your best baseball and just give up a big hit, the last thing you want is your best player to go down and get hurt," catcher Rod Barajas said. "We were very fortunate it wasn't a bigger deal."

Pittsburgh's starters have posted a 4.98 ERA in August -- nearly a run higher than their 4.03 ERA in the season's first four months -- and awful starts have been the primary problem. The Pirates have fallen behind in 19 of their 22 games this month, surrendering first-inning runs 14 times.

Jeff Karstens (4-3, 3.79 ERA) has been the best of that struggling rotation in August, going 1-1 with a 3.60 ERA in four outings. He held St. Louis to two runs and two hits over seven innings Sunday in the Pirates' 6-3, 19-inning win.

Karstens is 2-1 with a 2.12 ERA in five starts at PNC Park this season, and he might need to put up some zeroes to beat Milwaukee. The right-hander is 0-5 with a 4.21 ERA in eight career starts against the Brewers, receiving a total of three runs of support while losing his past four.

Milwaukee counters with Marcum (5-3, 3.39), who will step onto a major league mound for the first time since developing stiffness in his surgically repaired elbow June 14 at Kansas City.

"He's a free agent after the season, and I think that's a time he needs to show people he can pitch," manager Ron Roenicke told the team's official website. "We all know he can pitch -- I've been watching him for a year and a half."

The Pirates have seen enough evidence. Marcum held them to a run and five hits over seven innings while fanning eight in a 5-1 home win June 2 -- the third time in five career starts against Pittsburgh he's gone that deep without allowing more than a run.

He's certainly fooling two of the Pirates' best hitters. McCutchen is 2 for 11 against Marcum while Neil Walker is 1 for 14.

Ryan Braun went 0 for 2 but walked three times Friday to raise his 2012 on-base percentage against Pittsburgh to .545, while Corey Hart continued his recent surge with three hits. The first baseman is hitting .424 (14 for 33) with 11 RBIs during a nine-game hitting streak.

It might be tough to extend that run Saturday. Hart is 2 for 19 lifetime against Karstens.