Mortensen Better, Believe It : Cross-country: After defending champion Julia Stamps drops out of the race, Thousand Oaks runner cruises and becomes region’s first girl to win national title.

Forget about trying to stay within 20 seconds of defending champion Julia Stamps of Santa Rosa High.

To heck with running for second place, period.

Kim Mortensen of Thousand Oaks shocked herself, her coach and spectators alike by winning the girls’ title in the Foot Locker national cross-country championships at Balboa Park’s Morley Field on Saturday.

“I don’t know how,” she said in disbelief. “This is unbelievable.”

Mortensen’s time of 17 minutes 12 seconds over the 5,000-meter course made her the first runner from the region to win the girls’ title.

Camarillo’s Eric Reynolds and Agoura’s Bryan Dameworth won boys’ championships in 1982 and ’89.

Mortensen had set seven course records and tied another while posting 10 victories this season. But she had finished a minimum of 19 seconds behind Stamps in four races, including the West regional championships in Fresno on Dec. 2.

Stamps failed to finish Saturday’s race, however, after battling a cold all week.

Nonetheless, she had a one-second lead over Mortensen after the first mile (5:18-5:19) and extended it to five seconds at the race’s midway point before Mortensen began to reel her in.

“After the mile, I figured, ‘Oh. OK. This is where Julia takes the lead,’ ” Mortensen said. “I just wanted to try to stay as close to her as possible.”

She did better than that, catching Stamps at the two-mile mark (11:06) and then surging into the lead.

“I knew if I was going to pass her, I had to be aggressive about it,” Mortensen said. “I didn’t want to go, ‘Ah, excuse me, Julia? Can I pass you?’ ”

At that moment, Stamps knew she was in trouble.

“At the mile mark, I could feel the lactic acid building up in my legs,” she said. “And when I heard the time at two miles, that just wasn’t me.”

Things got worse for Stamps as her legs turned to lead. She began to stagger on the course at about 2 1/4 miles before collapsing and being attended to by medical personnel.

With Stamps out of the race, Mortensen found herself with a lead of nearly 100 meters which she maintained to the finish.

Her 17:12 clocking gave her a 16-second margin of victory over runner-up Amy Yoder of East Noble High (Noblesville, Ind.) and a 21-second advantage over third-place Katy Radkewich of Beaumont High (Cleveland Heights Ohio).

“I never could have imagined that this would happen,” Mortensen said. “To win a race like this against athletes of this caliber is just incredible.”

Thousand Oaks Coach Jack Farrell agreed.

“This is not anything I considered,” he said. “I thought a second in this type of field would be phenomenal. A top-five finish would be wonderful and really, anything in the top 10 would be satisfying.”

Although Stamps fell short in her bid to become the third runner to win two consecutive national titles, she praised Mortensen’s victory.

“Kim ran a great race,” she said. “I’m really happy for her. She’s run well all season and it’s nice to see her end it with a race like this.”

The Nordhoff duo of Will Bernaldo and Elaine Canchola fell short in their bids for top-10 finishes.

Bernaldo was in eighth place after the first mile of the boys’ race, but finished 22nd in 15:49. Abdul Alzindani of Fordson High (Dearborn, Mich.) won in 15:12.

Canchola went out conservatively in the girls’ race and moved up to 13th at the midway point, but a cramp slowed her to 26th in 19:17.

“I felt good for the first half of the race,” Bernaldo said. “But then I lost my focus. . . . And once you lose it, it’s real hard to get it back.”

Bernaldo, who finished a surprising seventh in the West regional, said he expected to produce another shocker.

“I planned to take one of the top spots,” he said. “But it didn’t happen. Today just wasn’t my day.”

It certainly was Mortensen’s.