Last year's Midwest League champions just wrapped up the East Division second-half crown.
Scott Sizemore doubled in the go-ahead run in the Whitecaps' 4-2 victory over visiting Great Lakes, 4-2, to take the division title.
"Our guys are doing a heck of a job," West Michigan manager Tom Brookens said. "It's a nice win. We're in the playoffs. We've accomplished the first step and now the ultimate goal is to win the championship.
Former Major Leaguer Brookens said his team got more focused after the Dayton Dragons won the first half in the division.
"You go out with something to prove," he explained. "We're clicking right now, we're playing good baseball and we're in the playoffs.
In the seventh inning, Jordan Newton drew a leadoff walk stole second and advanced to third on a groundout by Ryan Strieby.He tied the game, 2-2, on a single by Gorkys Hernandez.
Sizemore followed with a double and Newton added an RBI two-bagger in the eighth as the Whitecaps (45-21) recorded their fifth straight win.
West Michigan reliever Phil Napolitan (4-2) struck out four of the five batters he faced for the win. Luis Marte worked around a leadoff walk in the ninth to notch his third save. Starter Lauren Gagnier allowed two runs -- one earned -- on six hits while striking out four and walking three in 6 2/3 frames.
Juan Apodaca and Rick Taloa, who went 3-for-4, had RBI doubles in the fifth and sixth respectively for the Loons (21-43).
Great Lakes reliever Joseph Jones (1-3) surrendered three runs on three hits and four walks in 1 2/3 innings for the loss. Starter Joshua Wall scattered four hits with three strikeouts in five innings.
"[Wall's] got a good live fastball," Brookens said. "He's a big-league prospect in my mind."