(SportsNetwork.com) - The Pittsburgh Pirates may have to start thinking about capturing a wild card berth because they keep dropping out of contention for an National League Central title.

The Pirates have lost four in a row and will resume their 10-game homestand Friday with the first of three straight games against the Chicago Cubs at Wrigley Field.

Pittsburgh was just swept in three games at St. Louis, which leads the Central by 5 1/2 games over the Pirates. Peter Bourjos drove in the go-ahead run in the bottom of the ninth inning and Yadier Molina beat Andrew McCutchen's throw home for a 1-0 victory.

Neil Walker had three of Pittsburgh's four hits and starting pitcher Edinson Volquez threw 6 1/3 shutout innings for the no-decision. Mark Melancon was dealt the loss for giving up the game-winning run.

"They were just a little bit better than us every game," Pirates manager Clint Hurdle said of the series with the rival Cardinals.

The Pirates are just 1 1/2 games out of the second wild card berth in the National League and will also visit Philadelphia for four games on this trip.

Vance Worley takes the mound for the Buccos Friday and is 6-4 with a 3.01 earned run average. Worley ended a personal three-game losing streak in Saturday's 3-2 win over Cincinnati and allowed two runs - one earned - over 6 1/3 innings. The right-hander is 2-0 with a 2.08 ERA in three career starts against the Cubs.

Pittsburgh is 5-3 in Worley's last eight starts.

Meanwhile, the Cubs recorded a three-game sweep of the struggling Milwaukee Brewers with Wednesday's 6-2 victory, as Chris Valaika homered and Jorge Soler drove in a pair of runs.

"I was just looking for a good pitch to hit," Valaika said. "Something I could drive. I saw the slider well out of his hand, put a good swing on it and put us on the board."

Soler, who has hit safely in all seven games since making his major-league debut, has 10 RBI already and has only gone one game without driving in at least one run.

Kyle Hendricks picked up the win and allowed two runs in 5 2/3 innings for the Cubs, winners in nine of their last 13 games.

Tsuyoshi Wada gets the start for the Cubs Friday and the Japanese left-hander is 4-2 with a 2.79 earned run average. Wada is 4-1 in his last five decisions, but was beaten by St. Louis in Saturday's 13-2 defeat, allowing four runs -- three earned - and five hits in six innings.

Wada has never faced Pittsburgh and is 4-1 in six home starts.

Pittsburgh is 9-4 against Chicago this season and will host the Cubs for three games from Sept. 12-14 at PNC Park.