Matt Garza will start for the Brewers against John Lamb in Game 1, and Wily Peralta will face Keyvius Sampson in Game 2.
This was the Reds' fifth postponement of the season and their third at home.
It was Cincinnati's 21st rain delay of the season and the 15th at Great American Ball Park. The Reds have waited out 27 hours and 45 minutes' worth of delays this season, including 21 hours and 46 minutes at home.
"We've had interruption [before], but we haven't had necessarily the cancellations and just massive amount of time missed to delay," Reds manager Bryan Price said. "For a guy from the West Coast, now living in Arizona, this is extremely unusual."
Especially compared to the Brewers, who have endured only four delays impacting three games all season thanks to playing half their games under Miller Park's movable roof. Friday marked Milwaukee's first postponement.
"It's funny because after the game [Thursday] night, [Brewers bench coach] Jerry [Narron] said to me, 'A rainout would help tomorrow' because of the bullpen situation with some guys," said Brewers manager Craig Counsell, whose club was coming off a sweep of the Pirates. "I said, 'It's not going to rain tomorrow.'
"We've still got to play 18 innings tomorrow. It's part of it. We've been fortunate with the weather this year."
Fans holding tickets for Friday night's game may present their ticket at the gate for the rescheduled game Saturday night with no exchange necessary.
The ticket can also be exchanged at face value for any remaining 2015 home game except Sept. 12, subject to availability. Ticket exchanges are available at Great American Ball Park throughout the regular season in advance of game day only.
The severe rain and lightning interrupted what had been a clear, warm evening along the Ohio River. Following an 8:30 p.m. ET meeting, the game was officially postponed.
Adam Berry is a reporter for MLB.com. Follow him on Twitter at @adamdberry. Adam McCalvy is a reporter for MLB.com. Follow him on Twitter @AdamMcCalvy, like him on Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.