The All-Star centerfielder hit a solo home run off Cincinnati reliever Jonathan Broxton with one out in the ninth inning to lift the Pirates over the Reds 2-1 Saturday night.
Two innings after a powerful drive to left-center died at the wall, McCutchen took a 2-2 fastball from Broxton and sent it into the seats in right-center for his 31st homer of the season.
"I just kept running until it went out," McCutchen said.
A day after getting no-hit by Cincinnati's Homer Bailey, the Pirates won with eight hits. McCutchen was greeted by a mob of teammates after hitting Pittsburgh's third game-ending homer of the season, though he deftly avoided the brunt of a Gatorade bath while doing a postgame on-field interview.
"Wins have been hard to come by," said Pittsburgh manager Clint Hurdle. "We didn't let this one get away after we took the one-run lead and they came back and tied it in the eighth. We were able to answer back. It was a good team victory tonight."
Cincinnati, trying to keep pace with the Washington Nationals in the race for the National League's best record, again struggled to score runs.
The Reds wrapped up the NL Central earlier in the week but have now scored just five times in their last four games and now trail the Nationals by one game for homefield advantage throughout the playoffs.
"We want to make sure guys get their at-bats to try to get ready and get things rolling," said acting Cincinnati manager Chris Speier. "We still have some time. We'd sure like to see it turn around sooner than later."
A lone run on Friday was more than enough to preserve Bailey's gem, and a game-tying single in the eighth by Scott Rolen on Saturday appeared to the Reds life. The Pirates loaded the bases in the bottom of the inning off Cincinnati reliever Logan Ondrusek, but Starling Marte popped out harmlessly in foul territory.
Hanrahan came on in a rare non-save situation and worked around a couple of walks to get to the bottom of the ninth. Josh Harrison lined sharply to center to lead off the inning and McCutchen smacked a Broxton offering into the stands to help the Pirates improve to 77-81.
"That's the way it goes," Rolen said. "Hanrahan is out there. He's throwing the ball well. He's had a great year. There's no easy at bats when he's out there. We put something together and then they came back and got us there in the bottom."
Pittsburgh needs to win its final four games to avoid extending the longest losing season streak in North American professional sports history, and the Pirates' seventh walk-off win of the season improved their record to just 14-34 since Aug. 8.
Back then Pittsburgh was trying to track down the Reds for the division lead. The bottom fell out shortly thereafter and getting no-hit for the first time on Friday night provided an ugly exclamation point on a collapse that turned a once-promising season into one that would end without a winning record for the 20th straight time.
While the Reds focus on the playoffs, Pittsburgh is already working on next season.
Kyle McPherson, who is trying to get a jumpstart one of the open rotation spots in 2013, finally found some solid footing in his third big-league start. The 24-year-old failed to get out of the fifth inning in each of his previous two outings due to command issues that led to bloated pitch counts.
There were no such problems against the Reds. Cincinnati led off the first with a pair of sharply hit singles but couldn't score, and McPherson allowed just four hits over his six innings of work, striking five and walking just one.
"He's got to feel good about himself after tonight's performance," Hurdle said. "He went six innings through the Central Division champions lineup. He's got what you're looking for, you just have to sprinkle some experience on it."
Problem was, the Pirates couldn't get anything going off Mike Leake. Pittsburgh ended any chance of getting no-hit for a second straight night early when Josh Harrison singled with one out in the first, but otherwise Leake matched McPherson zero for zero as he tried to make a case for postseason playing time.
"I hope we stay in it for the whole time so that I can put some significant role into it," Leake said. "I've just got to hope I make it in the bullpen or hope we make it into the second round so I can play a role."
The series concludes on Sunday. Johnny Cueto (19-9, 2.83 ERA) starts for Cincinnati against Pittsburgh's Wandy Rodriguez (12-13, 3.79) ... The Pirates drew their 17th season sellout of the season on Saturday and topped 2 million in attendance for the fourth time in franchise history.