Maybe, just sometimes, Cheyenne Mountain's defense is too smothering on opposing girls' soccer teams. Perhaps that explains why a weak goal might sneak by every now and then.

Fortunately for the top-seeded Indians, by the time a Centaurus shot dribbled through and past Hunter Peifer, they had built a two-goal lead and hung on to beat the No. 9 Warriors 2-1 Tuesday in a 4A quarterfinal playoff.

"I got out of the game a little," said the Cheyenne Mountain sophomore goalie, who has been in net for 11 shutouts this season. "I'm not going to lie, sometimes you daydream a little. Some games, I'll see a million shots. Some games, there are none. That ball kind of skipped and went through, and there's no excuse for that, but the team stepped up and supported me, and I'm more focused on a big win."

Aspen Peifer, Hunter's older sister, scored both goals for Cheyenne Mountain (15-2-1), who advanced to the 4A state semifinals for the first time since 2010. The Indians will play either league foe Air Academy or get a rematch against Valor Christian, who has won the last two meetings, including a road win in last year's quarterfinal for Cheyenne Mountain's only loss of 2012.

Not quite midway through the first half, Hunter Peifer unleashed a long goal kick, its second bounce taking it well into the Centaurus (10-3-3) box. Goalie Kathy Tran ran up to corral the bounce, but senior center back Caity Hughes also called for it. The result was a misplayed ball. Aspen Peifer pounced on the turnover and converted it into an easy goal.

"It was just a misunderstanding," Hughes said. "I was in front of the goalie, and I called it, then she called it. All it takes is one mistake and it throws you off."

With 2:01 gone in the second half, Aspen Peifer took possession in the open field, some 35 yards away from the goal. With no one approaching, she had plenty of time to plant her right foot into a high, arcing shot that eluded a leaping Tran and gave the Indians a 2-0 lead.

"I saw a bunch of defenders kind of in the back, and the goalie stepped off her line," the senior forward said. "I thought I might as well have a go at it. It fell for me this time."

Centaurus, which scored 10 goals in its first two playoff games, struggled to gain and keep possession to mount serious scoring chances. Outside of the goal scored by Danielle Dondelinger with 14:16 left, the Warriors had only one other great opportunity.

Seven minutes before, freshman Jamie Turcotte maneuvered to the upper right corner of the penalty area, sending a high shot toward the net. However, Hunter Peifer jumped and punched the ball out with her right hand, and the rebound was directed well wide of the net.

"In our first two games, they had one forward that was the main attacker," Hughes said. "Cheyenne Mountain has three people up front, always attacking. Our defense had to figure that out, and it caught us off guard a little."

Now, the Indians are headed to Sports Authority Stadium in Parker for Saturday's semifinal game, set for 11 a.m. A win there would put Cheyenne Mountain in position to win its fourth state title and first since 2007.

"Centaurus had the right plan by sitting back, and we were getting frustrated," Indians coach Tomas Martinez said. "I was worried we'd make a mistake and they'd have a counter the other way. But we're on to the semifinals, and that's all we can ask for. It's time to get back after it and do what we need to do."