Riverside knotted the score in the top of the third with the help of the Cougars' first error and an RBI single by Chaz Davis.
The Warriors took their first lead in the fifth when pinch hitter Cameron Green led off with a double and came around to score on a two-out, RBI double by Aaron Halstead. Halstead scored two batters later on an RBI single by Derik Chestnut.
After trading runs in the sixth, Riverside opened a 7-4 lead in the seventh when Tyler Hall scored on another Capital error, followed by an RBI single by Drew Mack that plated Cameron Norris. Mack was 3-for-4 with a double and an RBI.
The Cougars made things interesting in the home half of the seventh, turning a hit batsman, two errors and a pair of walks into two runs to cut the lead to 7-6, with two outs and the bases loaded.
Senior Tyler Hall came on to end the Cougars' threat by striking out Kincaid to end the game.
The loss was yet another stinging defeat for Capital, which lost by one run for the sixth time in nine losses.
"It's really getting old, but we're going to continue to go through and keep plugging along," Capital Coach Robert Massey said. "The biggest thing I was not pleased with is that we're not even playing the bottom of the seventh inning if we don't make errors. We had four or five errors and I know it cost us at least three runs."
Massey was pleased with the performance of junior right-hander Austin Hupp.
Hupp, making his first start of the season, gave up 12 hits, while striking out five and allowing just one walk.
"Austin Hupp gave probably one of the gutsiest performances I've had up here in seven years," Massey said. "I looked at him and said 'Buddy we ain't got anybody else. It's you or nothing,' and he went and he gave us everything he had.
"You just have to take your hat off to him."