Walker’s hit off of Aroldis Chapman (2-1) was his third hit of the game, and Brandon Wood followed with an RBI double, allowing Pittsburgh to improve to 8-3 against the Reds this season.
Charlie Morton continued his mastery of Cincinnati with six effective innings, and McCutchen and Ryan Ludwick each had two hits for the Pirates, who have won three of five.
Joey Votto twice drove in Brandon Phillips with RBI singles for the Reds, who have lost four of six. Phillips reached base four times.
Recalled from Triple-A Indianapolis earlier in the day, rookie Tony Watson (1-2) won his first major league game by getting the final two outs of the top of the seventh after the Reds had tied it at 3 against Chris Resop.
Pittsburgh’s Jose Veras pitched a scoreless eighth — striking out Drew Stubbs and Dave Sappelt after allowing the first two batters of the inning to reach. A day after allowing a season-high three runs in taking the loss, Joel Hanrahan worked a perfect the ninth for his 31st save but first since July 28.
Morton had a scoreless innings streak of 24 snapped in the final inning of his most recent outing on Sunday when Hanrahan allowed an inherited runner to score.
Morton allowed a run for the second consecutive inning when Phillips led off Saturday’s game with a single, moved to second on a groundout and came home when Votto singled to right.
But Morton faced only one over the minimum over the next 4 2-3 innings before Phillips and Votto each singled again to produce a run in the sixth.
RBI singles by Ronny Cedeno in the fourth and Ryan Ludwick and Walker — consecutively in the fifth — gave Pittsburgh the lead, and Morton was in line to improve to 4-0 against Cincinnati this season after he was lifted following six innings.
Morton was charged with two runs on seven hits, a walk and two strikeouts. He is 3-0 with a 0.93 ERA in 29 innings against the Reds this season.
But the Reds quickly tied the game against Resop when Ramon Hernandez doubled in Stubbs.
Cincinnati’s Dontrelle Willis remained winless in eight starts this season, allowing three runs on eight hits and three walks in six innings.
NOTES: Not counting the 2006 All-star game, the game was the first televised by Fox at PNC Park since 2004. ... The crowd of 37,826 was Pittsburgh’s 16th sellout of the season, most since 2001. It was the eighth consecutive Saturday sellout there. ... Reds Sunday starter Mike Leake has allowed only seven earned runs in five career starts against Pittsburgh. No current Pirates players have homered off of him. ... The previous time Pirates RHP James McDonald faced Cincinnati on July 19, he pitched into the seventh and was part of a combined shutout. McDonald starts Sunday.