The Loons built a three-run lead behind starting pitcher Zach Lee and held on for a 6-5 win over the Lansing Lugnuts at Cooley Law School Stadium.
The Lugnuts scored single runs in the sixth and seventh innings and then a two-run home run from right fielder Michael Crouse in the eighth, but Lansing couldn't push any runs across to tie or win the game in the bottom of the ninth.
The Loons took the first game of a key early-season three-game series that features the top two teams in the Eastern Division of the Midwest League.
The Lugnuts remained in first place at 11-5 despite Monday's loss - which ended their five-game winning streak - while the Loons are right behind them at 11-7.
Lansing will play the Loons in the second game of a the series at 7:05 p.m. today at Cooley Law School Stadium.
The Lugnuts scored in the first inning on Oliver Dominguez's RBI groundout, and Lansing starter Casey Lawrence was pitching even better than his Great Lakes counterpart early in the game.
Then the Loons broke it open in the top of the fifth inning.
Second baseman Bryant Hernandez and shortstop Christian Lara each hit two-run doubles as part of an inning that saw four Loons cross the plate.
Great Lakes first baseman Blake Dean added a two-RBI double in the top of the seventh to help negate Lansing's attempt at a comeback.
The Loons helped the Lugnuts out, with two errors leading to two Lansing runs in the sixth and seventh innings.