In a performance that minimized the importance of homework, Kate Robinson pitched a perfect game, boosting the University of Hawai'i softball team to an 8-0 victory over New Mexico State and a doubleheader sweep yesterday at Rainbow Wahine Stadium.

The game was called in the bottom of the sixth because of the eight-run mercy rule, leaving Robinson one short of the school record of 15 strikeouts.

Justine Smethurst pitched a five-hitter as UH won the opener, 2-0.

The sweep helped the Rainbows remain in first place in the Western Athletic Conference with a 7-1 record. UH is 23-14 overall. New Mexico State fell to 22-15 and 5-4.

Robinson, a sophomore from the Kamehameha Schools, was not told she would start until the sixth inning of the first game.

"Nobody knew who was starting until then," she said. "I didn't have a lot of time to think about it."

UH coach Bob Coolen said he had planned to use Robinson as the first reliever if Smethurst struggled in the opener. With Smethurst in control, Coolen, in consultation with pitching coach Dana Degen, opted to give Robinson her first start of the season.

"She deserved it," Coolen said.

Robinson dominated the Aggies, striking out 14 of the 18 batters she faced. Of her 72 pitches, 55 were strikes. She had a three-ball count on only one batter.

Robinson's best pitch is a downball, which she releases from behind her hip. "You can't see where it's coming from or where it's going," Coolen said.

Catcher Kristi Yoshizawa, who called the game, noted that all of Robinson's pitches "were working. I think that's what got them. We were mixing them up. They didn't know what was coming or what to expect. Her dropball is her best pitch, but honestly, I was barely using it. We were sticking with curves and risers."

Robinson threw curves to the left-handed batters. Coolen said Robinson's risers, which tailed away from right-handed hitters, zipped along at up to 65 mph, the equivalent of a 92-mph pitch in baseball.

"Watch her finger work," Coolen said. "When she throws her riseball, she brings it so hard that it hops. That's what you want. You want that wrist and the finger roll to make it hop. All of her pitches hop. That's her success."

Robinson said she put her trust in Yoshizawa.

"She always calls a good game," Robinson said. "She reads batters really well. It's fun pitching for her."

Despite the lack of preparation time with Robinson, Yoshizawa said, "I know her really well. We're good friends. I catch her a lot in practice. I know what to call, and what she's like, and she lets me make the calls."

As the game progressed, Yoshizawa adhered to one of the sport's oldest rules: Don't inform a teammate she's throwing a no-hitter.

"I didn't even want to talk to her," Yoshizawa said. "I didn't want to mess her up. I wanted to leave her where she was, and she did really good."

Robinson avoided a dramatic finish when Brandi Peiler and Tyleen Tausaga hit consecutive home runs to left-center field to trigger the mercy rule.

"I wanted to go to the (seventh) inning so she could try for the strikeout record," Tausaga said.

But the abbreviated game probably was best for Tausaga, who had fouled a pitch against her right leg. Because of the hurry-up rule — a pitcher has 10 seconds to throw the next pitch — Coolen had to call timeout, allowing Tausaga to try to walk off the pain.

"That sort of thing stings," Coolen said.

Reach Stephen Tsai at stsai@honoluluadvertiser.com.