With their eighth win in 10 games, the Pirates kept pace with their prime postseason competition, as Milwaukee and St. Louis both registered wins. The Brewers remained 1 1/2 games behind the Bucs for the National League's No. 2 Wild Card, while the Cardinals retained their 3 1/2-game Central Division lead.
Most responsible for keeping the status quo was Harrison, whose defensive play provided the biggest momentum changer imaginable.
A sellout crowd of 37,655 had been kept silent for three innings by Chicago right-hander Jacob Turner as his mates built a 3-0 lead over Edinson Volquez.
"It was definitely the tipping point of the game," said Pirates manager Clint Hurdle.
"It was huge. It fired up people. After that we were ready to go," said Andrew Lambo, the trainee first baseman who found himself on the finishing end of a triple play in his very first big league game at the position.
"We were in a spot where we were playing just flat for the first several innings," said second baseman Neil Walker, the middleman. "All of a sudden, that kind of momentum carried over into the offensive side of things."
First on the flip side was Walker, who with one out in the fourth found the center-field bushes with his 20th homer -- breaking his tie with Bill Mazeroski (1958) for the most ever by a Pittsburgh second baseman.
"Record-breaking homer, or triple play?"
"Regardless," laughed Walker, breaking up over the preference query, "it was a pretty cool day."
Seconds after gloving Matt Szczur's hard grounder with men on first and second and none out in the fourth, Harrison was dashing into the Bucs' dugout, with an exhorting fist pump.
"You could feel it right away, as soon as we turned the triple play," Harrison said. "Then Walker hits the home run. We do a good job of not letting whatever happened affect us. We just kept pushing."
The aftermath of this triple play was a bit better than the last time the Bucs had gone around-the-horn on a triple killing. After bouncing into that in the nightcap of the July 23, 1979, doubleheader at Three Rivers Stadium, Braves righty Phil Niekro went on to complete a two-hit shutout.
This time, the Pirates grew offensive fangs immediately to chew up the Cubs' 3-0 lead.
Walker's opening salvo was a mere prelude: The Pirates sent 12 men to bat in the fifth, a six-run inning detonated by Harrison's two-run double.
"Walker sparked us with the homer, then we connected some dots and did some nice things on offense," Hurdle said. "We covered some balls up that we weren't covering earlier. We weren't finding the barrel until Walker's homer."
Walker was somewhat sheepish in discussing having broken a Mazeroski record.
"I haven't really thought that much about it. As I've said before, I'm humbled just to be in the same breath as other people on that list. To get to this point is very humbling ... and I'm happy that I got there."
The Cubs had taken advantage of Volquez's throwing error to score twice in the second, and stretched their lead to 3-0 in the third on the rare combination of a seeing-eye single and a seeing-eye throw. First, Javier Baez perfectly placed a grounder between Harrison and shortstop Jordy Mercer. Then, on Baez's steal of second, catcher Russell Martin's throw sailed between Mercer covering the bag and Walker backing up.
The throwing error sent Baez to third, in position to score on Chris Coghlan's sacrifice fly.
It only seemed to be getting graver for Volquez in the fourth -- before Harrison came to the rescue and flipped a switch.
"I've said before ... he can do everything. He's a great player, man," Volquez said. "He saved that inning, gave me a chance to get out of there, then I was able to shut it down and make better pitches the last four innings."
Volquez threw shutout ball for the remainder of his seven-inning stint as he ran his spotless lifetime record over the Cubs to 7-0. In earning his 12th win of the season, he allowed one earned run and four hits, while working his way around five walks and striking out five.
"[Harrison] helped Edinson out," Hurdle said. "He found a 'go' button and got into a real good lane. Five, six, seven -- he really pitched well."
After five losses in six games and 10 days to the Pirates, Chicago manager Rick Renteria left town impressed.
"They're a very good ballclub," Renteria said. "They've got the components of pitching and the offense and they play really good defense. They make plays when they need to and they get big timely hits when they need to. You've got to grind them out."