"I knew he would play a huge role in this," manager Bruce Bochy said. "And I know of other situations where starters have been in the 'pen and really done a great job to help their team win. We knew Timmy would play a critical role in the series like he did tonight."
The Giants can complete an unprecedented comeback on Thursday. No team has recovered from a 2-0 deficit in a best-of-five series by winning three on the road, according to STATS LLC.
"Thanks to the win today, there will be a tomorrow," Pagan said. "And we are ready for that."
Matt Cain, who lost the series opener and has yet to beat the Reds in three tries this season, will start Game 5 against Mat Latos.
The Giants' hitters emerged from a series-long slump and extended Cincinnati's playoff misery. The Reds haven't won a postseason game at home in 17 years.
One thing in the Reds' favor they haven't dropped three straight at home all season.
"I'd like to think that we still have the advantage," Reds outfielder Jay Bruce said. "We're at home. I expect Mat to come up with a big game. I'm looking forward to it."
The Reds were hoping to start ace Johnny Cueto, but had to drop him off the roster a few hours before Wednesday's first pitch because he was still bothered by a strained muscle in his right side.
He won't be available if Cincinnati wins Game 5 and reaches the NL championship series.
The way the Giants have started hitting, that's now in doubt.
San Francisco managed only four runs in the first three games of the series.