Second baseman Neil Walker led the assault with a pair of homers off Cincinnati starter Bronson Arroyo, with Andrew McCutchen, Pedro Alvarez, Marlon Byrd and Andrew Lambo also clearing the fences for the visiting Pirates.
The win improved Pittsburgh's record to 93-68 and dropped the Reds to 90-71 with one game remaining in the regular season.
It also assured the Pirates' long-suffering fans their first home playoff game in Pittsburgh in 21 years in a do-or-die showdown contest for entry to the best-of-five Division Series.
In the American League, a close three-team race for the last two postseason berths grew even tighter with Saturday's results.
The visiting Tampa Bay Rays lost 7-2 to the Toronto Blue Jays, while the Texas Rangers beat the Los Angeles Angels 7-4 to tie Tampa Bay in the wild card standings at 90-71 with just one more game to play.
The Cleveland Indians (90-70) were suddenly in the driver's seat, playing the Minnesota Twins (66-94) with a chance to forge ahead in the standings or join a three-way tie.
Should there be a three-way tie in the American League wild card race, the Indians would host the Rays on Monday with the winner claiming one wild card spot.
The loser would travel to Texas to play a do-or-die contest against the Rangers on Tuesday for the second wild card spot. The wild card winners would battle on Wednesday with that winner advancing to the best-of-five Division Series.