Jeff Locke tries to help the Pirates win the pivotal three-game set and potentially wrap up a long-awaited postseason berth with another impressive performance against the Reds on Sunday.Pittsburgh (89-66) was 3 1/2 games ahead of Cincinnati last Sunday but dropped into a tie atop the wild-card standings Friday by blowing a late three-run lead in a 6-5 loss in 10 innings.The Pirates rebounded by rallying from an early two-run deficit Saturday for a 4-2 win and remained within two games of St. Louis in the NL Central while taking their slim lead over the Reds (88-67).Marlon Byrd, acquired along with Justin Morneau in late August for the postseason drive, hit a tiebreaking sacrifice fly in the sixth inning. The Pirates' second victory in six contests ended the Reds' four-game win streak.Locke (10-6, 3.27 ERA) will try to move his team a step closer to clinching its first playoff berth since 1992 by improving to 3-0 all-time against Cincinnati. The left-hander has a 1.19 ERA in four career starts against the Reds and is 2-0 with a 1.00 ERA in three matchups this season.Locke, though, is 1-4 with a 5.90 ERA in 10 outings since a 3-2 win in Cincinnati on July 21. He gave up four runs over five innings in a 5-2 loss to San Diego on Tuesday."This ain't no different than all the other starts," Locke said. "Just falling behind early and getting behind."If Locke can earn another victory over the Reds, there's a chance Pittsburgh could secure its first trip to the postseason with some help. Along with a win, the Pirates would need Miami to sweep Sunday's doubleheader against Washington.Bronson Arroyo, meanwhile, will try to reduce the Reds' magic number to the playoffs -- currently at four -- by earning his first win since Aug. 24. He is 0-2 with a 4.56 ERA in his last four starts but has allowed two earned runs or fewer in each of his last three.Arroyo (13-11, 3.56) gave up two runs and three hits over 6 1/3 innings in Milwaukee last Sunday but the Reds bullpen collapsed in a 6-5 defeat."That's probably as crushing of a defeat as we've had all year," Arroyo told the team's website.Arroyo is 0-3 with a 6.14 ERA in his last four starts against Pittsburgh but allowed only one run over seven innings in his only matchup this season, a 2-1 victory June 19.Byrd is 8 for 21 (.381) with a home run and two doubles all-time against Arroyo and will face him for the first time this season. The right-hander needs to pitch at least 7 2/3 innings to record 200 or more for the eighth time in nine seasons.Three of the Reds' top hitters -- Joey Votto, Jay Bruce and Brandon Phillips -- are a combined 2 for 21 against Locke in 2013. Another one of their top hitters, Shin-Soo Choo, was forced to sit out Saturday after injuring his right hand in the series opener, and his status is unknown for upcoming games.