Justin Miller drove in the game-winning run with an RBI single in the eighth inning, as the Ems took the first game of the series 5-4 on Thursday night at PK Park.
The win moves the Emeralds one game behind Salem-Keizer for second place in the Northwest League's Western Division.
"It's great to play close games this time of year and practice how we're going to have to play at the end," manager Pat Murphy said. "Like you guys have been saying, you can't just take the second half off. You've got to compete.
"They're developing because they're learning to play close games, they're learning to play baseball, and they're learning that these games do mean something. It's their career and there's only one way to play, and that's winning baseball. Happy for them."
After being retired in order in the sixth and seventh innings, the Ems took advantage of Volcanoes relievers who fell apart in the eighth inning.
Matt Graham entered the game and retired the first hitter he faced.
The side-armer, McCormick, threw a pitch behind the batter, Jose Dore, allowing the tying run to score.
McCormick would retire Dore on a ground out, but it allowed the pinch runner, Jace Peterson, to move to third base.
Next at the plate was Miller, and he drove a fastball, scoring Peterson and giving the Ems a 5-4 lead.
"He just came fastball away," Miller said. "I knew the type of pitcher he was—he was just going to leave it out there. I fouled off the first one and he came back with another one, and got that one through the hole."
Miller, who went 2-for-5, also extended his hit streak to 12 games.
"I didn't even know I had it until game ten, so it's going good," he said. "Just trying to keep consistent and put good swings on good pitches and let it play itself out."
Nursing a one-run lead, Chris Wilkes recorded the save and capped off an impressive outing by the bullpen, which allowed only one hit during the final four innings.
The Eugene pitching combined to relatively silence three Volcano hitters who rank No. 1, No. 2 and No. 3 in the Northwest League in average.
"Well, they're a good ball club," Murphy said. "That's all there is to it. They're a great offensive ball club and their pitching this time of year has got them in a position to be second-half champs.
"They're definitely very capable and they're a very, very good ball club… I fear them as much as anybody. They're an explosive offensive club and are capable on any night."