River City opened the scoring in the second inning on a run-scoring double play off the bat of Gerrion Grim.
Evansville tied the game in the fourth on a Manny Cruz RBI single.
River City retook the lead with a three-run seventh. Zach Lavy scored on wild pitch from third to break the tie, and then Connor Oliver drilled a two-run homer to put the Rascals up 4-1.
Evansville got one run back in the eighth when Toby Thomas hit a solo shot to left, his fifth of the year.
The Otters inched to within one in the ninth after a David Cronin RBI ground out, but fell 4-3.
Tyler Vail was solid for the Otters as he tossed 6.1 innings, allowing just two runs and striking out six, but is hung with his second loss of the season.
Hector Hernandez gets the win, his fourth of the year for the Rascals. Hernandez threw seven innings, giving up two runs, one earned, while striking out five.