The Bucs initially overcame the 3-0 hole dug in the first inning by Liriano, but that merely set in motion a give-and-take game they ultimately dropped.
"We've got a lot of come-from-behind victories. Today was just a case where they threw some punches back," Neil Walker said.
Rookie lefty Bobby LaFromboise had inherited a bases-loaded, one-out jam from John Axford in the 10th and recovered from a 3-0 count to get pinch-hitter Brayan Pena on a shallow fly before being taken deep by Santiago, who had only one prior home run this season in 179 at-bats. It was also the 13-year veteran's first career grand slam.
"It was good [the way LaFromboise got Pena], and you think you got a chance," manager Clint Hurdle said. "You try to hang on and find a way to play another inning, and it didn't work out.
"In late innings, as we all know, walks never turn out to be your friend."
Axford, the fifth reliever called on in the wake of a short Liriano start, struggled out of the bullpen gate in the 10th. He walked the first man he faced, Todd Frazier, on four pitches. Axford survived a Devin Mesoraco smash to the center-field warning track for an out, but Chris Heisey followed with a solid single and Ryan Ludwick walked on a 3-2 pitch to sound the call for LaFromboise.
After surfing an emotional wave all day, the Pirates were about to get wiped out.
"Wonderfully crazy, like the season," Hurdle described this 161st game. "We got down, scratched back, got ahead -- they fought their way back in. It just goes to show you -- teams are always going to play and compete."
The 75-86 Reds embraced their cameo on the postseason scene-setter in the season's penultimate game.
"They obviously had a better season than we did," said Mesoraco, "but you still want to go out there and compete and do your job. We're still getting paid. We're not just here on our own having fun. We have a job to do and you have to go out there and compete and do the best you can. Hopefully we can throw a wrench in their plans."
It was a high-wire act for Liriano, who had been flawless for a month, sporting an 0.69 ERA over his last six starts.
Liriano allowed four runs (three of them earned, as many as the total in his prior six starts). Fives were wild: In five innings, he gave up five hits and five walks and also struck out five.
Jordy Mercer's homer and Walker's two-run single added up to a three-run fifth and a brief 4-3 lead erased in the bottom of the inning by Ludwick's two-out RBI single.
Two innings later, the Pirates broke that tie as Andrew McCutchen delivered a two-out RBI single off Sam LeCure and scored on Walker's triple.
The Reds crafted another tie in the bottom of the seventh against John Holdzkom, who proved to be human by giving up a two-run homer to Frazier that tied it at 6. Those were the first runs given up by the 6-foot-7 rookie, who was appearing in his ninth game.
"It was a ball up and out over the plate," Hurdle said. "This is the big leagues; those kinds of things will happen to guys if you continue to give them the ball."
"Still, this is one of the parks where that ball reaches the seats."
Walker called it "a Great American Ball Park home run," referring to the yard's long ball friendly dimensions and air currents.
The Pirates retained their slim hopes of still smelling the thin air of a division co-championship Sunday -- which, of course, would be resolved with a Monday tiebreaker game in St. Louis.