With the Nationals up 1-0 in the top of the eighth inning, Eaton delivered a two-run double on a full-count pitch from right-hander Adam Wainwright after going hitless in his first three plate appearances.
Eaton said he drew inspiration from George Costanza during the critical at-bat.
"Everything I was thinking, they did the opposite," he said postgame, according to ESPN. "So I was thinking 3-2 (count) should be a heater here and I'm like, well, that's the opposite, so I should George Costanza it and just go ahead and said breaking ball, and that's what happened."
The 30-year-old was referring to the "Seinfeld" episode called "The Opposite," where Costanza decides to do the opposite of his instincts.
"George was right and I happened to be right," Eaton said.
Game 3 of the series takes place in Washington on Monday, with the Nats looking to take a 3-0 advantage and push the Cards to the brink of elimination.