VANDALIA, Ill. • Mia Stack provided the power, and Alexis Silkwood supplied the arm for Alton Marquette on Wednesday afternoon.

Stack hit a grand slam, and Silkwood tossed a two-hitter as the Explorers defeated Gillespie 9-1 in the semifinals of the Illinois Class 2A Vandalia Sectional.

No. 3 in the STLhighschoolsports.com large-schools rankings and No. 6 in the Illinois Coaches Association Class 2A state poll, Marquette improved to 34-2.

The Explorers will play either Robinson (21-8) or Greenville (24-12) at 11 a.m. Saturday in the finals. Robinson and Greenville square off at 4:30 p.m. today in the other semifinal.

“Yeah, it looked pretty good,” said Stack, who swatted her third home run of the season. “We were expected to go outside, but she kept throwing inside. So we've got to with it. I guess she didn't hit her corner. And it was just kind of there.”

"Her" was Gillespie right-handed pitcher Laura Halpin (23-6), who surrendered five runs in the top of the second, four coming from Stack's hit. She now has 46 RBI.

Halpin threw an 0-2 pitch to Stack, who promptly lost it far beyond the leftfield fence to give Marquette a 5-0 lead. The Explorers had scored one run before that when Halpin issued a bases-loaded walk to Madeleine Youngblood.

“We had a lot of good at-bats before I was up,” Stack said. “Without those, we probably wouldn't have been able to do that.”

The runs were really all Silkwood (34-2) needed. She was perfect through 4 1/3 innings before Allie Goldasich singled to left. Then with two outs, Loni Manalia got a bloop single to right-center when centerfielder Anna Morrissey and Youngblood collided. But Silkwood struck out Alexis Burns swinging to end the threat.

Marquette added another run in the fourth on a leadoff double by Anna Morrissey and a sacrifice bunt by younger sister Claire Morrissey as Anna moved to third. Silkwood then delivered a sacrifice fly to right.

The Miners then ruined Silkwood's shutout in the bottom of the sixth when Halpin coaxed a walk from Silkwood and went all the way to third on a passed ball by catcher Morgan Wiedman. Molly Gray grounded out to second as Halpin scored.

The Explorers added three more in the top of the seventh — their lone run in the sixth on two hits, a walk, a hit batter and a ground out. Halpin allowed seven hits and seven walks with only one strikeout.

Silkwood gave up just two hits and a walk with 10 strikeouts.

“I knew they were going to get better as the game went on,” Silkwood said. “I knew I couldn't be throwing good pitches.”

"Two strikes, two outs ... You don't throw it right down the middle," Gillespie coach Michelle Smith said. "We can't blame it on Laura either. We've got to put a ball in play.”