John Hester's grand slam in the eighth inning powered the Missoula Osprey over the Billings Mustangs, 6-4, on Friday in the opener of their best-of-3 Pioneer League playoff series.
Hester, who homered and drove in four runs in the Osprey's regular-season finale on Thursday, erased a 4-2 deficit with a blast to left-center field off Terrell Young (0-1).
"It was a fastball up in the zone on a 1-2 count," Hester said. "I hit it pretty hard, but it was on a line, so I wouldn't say it was a no-doubter. But I had a pretty good feeling it was going out."
Daniel Stange pitched around a two-out walk in the ninth for the save as Missoula moved within one win of advancing to the best-of-3 Championship Series. The Osprey visit Billings for Game 2 on Saturday.
"Billings is a difficult place to play, not just for us but for any team in the league," Hester said. "Getting Game 1 here at our place, we definitely needed to do it. We went in knowing that and we made it happen."
Clay Zavada (0-1) picked up the win in relief, allowing a run on three hits and a walk with six strikeouts in 3 1/3 innings.
Missoula's Osbek Castillo had his worst start in more than a month, yielding three runs on four hits and four walks in 4 2/3 frames. He had allowed one run over 37 innings while striking out 53 in his last six regular-season outings.
"Billings is a good hitting ballclub and they have some polished hitters from the college ranks," Hester said. "We knew it was going to be a battle. You can't expect (Castillo) to shut out everyone he faces."
Drew Stubbs and Juan Francisco homered off Castillo as Billings built an early 3-0 lead.
"You can't expect someone to be on a roll forever," Hester said of Castillo, who allowed two homers all season. "We never really gave up offensively and (Castillo) kept us in the ball game. He never let get things out of control."
Billings starter Jordan Smith tossed five scoreless frames before Daniel Perales got the Osprey on the board in the sixth with a two-run shot off Jeremy Burchett.
Daniel Dorn delivered a pair of RBI singles for the Mustangs.
Carl Dispoto is a contributor to MLB.com. This story was not subject to the approval of the National Association of Professional Baseball Leagues or its clubs.