PITTSBURGH -- Starling Marte's sacrifice fly in the eighth inning gave the Pittsburgh Pirates a 5-4 victory over the Cubs on Tuesday in the first game of a day-night doubleheader that extended their lead over Chicago in the National League wild-card standings.

With the score tied at 4, first baseman Pedro Alvarez drew a leadoff walk from reliever Justin Grimm (3-5) to start the eighth. Pedro Florimon ran for Alvarez, stole second and continued to third on catcher Miguel Montero's throwing error before scoring on Marte's line drive to left field.

Marte, the Pirates' regular left fielder, entered the game in the seventh as a defensive replacement with Pittsburgh leading 4-1. He did not start for a third straight game while recovering from stomach flu.

Left-hander Tony Watson (4-1) pitched a perfect eighth for the win and closer Mark Melancon worked a 1-2-3 ninth to tie the franchise record with his 46th save in 48 opportunities. Mike Williams set the mark in 2002.

With their sixth win in seven games, the Pirates (87-56) moved five games ahead of the Cubs (82-61) for the first wild card and also got within two games in the NL Central race of the first-place St. Louis Cardinals, who play Tuesday night at Milwaukee.

The Cubs, who lost their third straight game, tied the score at 4 during a three-run seventh when they chased Pirates right-hander Gerrit Cole, who was unable to notch his 17th win.

Pinch-hitter Tommy LaStella's RBI double drew the Cubs within 4-2 and prompted Pirates manager Clint Hurdle to replace Cole with right-hander Joakim Soria, who allowed two runs to score on wild pitches.

Cole gave up four runs (three earned) and six hits in 6 1/3 innings with eight strikeouts and no walks.

Cubs right-hander Jason Hammel failed in his bid to win consecutive games for the first time since June 1 and June 6, getting tagged for four runs and five hits in 3 2/3 innings with five strikeouts and three walks.

Pirates center fielder Andrew McCutchen had two hits, as did Montero for the Cubs.

After right fielder Chris Coghlan put the Cubs ahead 1-0 with a sacrifice fly in the top of the first, the Pirates answered with three runs in the bottom of the inning as McCutchen hit an RBI single and left fielder Travis Snider had a two-run single.

Second baseman Neil Walker's run-scoring double in the fourth pushed the Pirates' lead to 4-1 and knocked Hammel out of the game.

NOTES: The Pirates selected the contract of RHP Vance Worley from Triple-A Indianapolis to add bullpen depth and designated RHP Radhames Liz for assignment. Worley was 3-1 with a 2.38 ERA in five starts for Indianapolis after being designated for assignment earlier in the season. ... Cubs INF Starlin Castro started at second base over INF Javier Baez as he entered the game 5-for-13 in his career against Pirates RHP Gerrit Cole. ... Cubs LHP Jon Lester (9-10, 3.50 ERA) will face Pirates LHP J.A. Happ (9-7, 3.87) in the second game. Happ has won his last five starts.