EUGENE, Ore. (AP) -- Qualifying medalists Amanda Blumenherst and Stephanie Na each won two matches Thursday to advance to U.S. Women's Amateur quarterfinals.

Blumenherst, the Duke star from Scottsdale, Ariz., beat Nikki Koller of Lewisburg, Ky., 4 and 3 in the second round and routed Ellen Mueller of Bartlesville, Okla., 7 and 6 in the third round at Eugene Country Club.

"When I get on a roll, I just keep going and it's easier for me," Blumenherst said. "I'm confident in my game. I'm hitting it really well and playing really solid and the putts are falling in, which is wonderful."

The 19-year-old Na, from Australia, beat Sydney Burlison of Salinas, Calif., 2 and 1 in the morning and Kristina Wong of Vestal, N.Y., 1-up in the afternoon.

On Friday morning, Blumenherst will play Spain's Carlota Ciganda, a 2-and-1 winner over Jennifer Hirano of Pinole, Calif.

In the other lower-bracket quarterfinal, Erynne Lee of Silverdale, Wash., will face Chelsea Stelzmiller of Placerville, Calif. Lee beat Canada's Kira Meixner in 19 holes, and Stelzmiller beat Megan McChrystal of Stuart, Fla., 2 and 1.

In the upper-bracket quarterfinals, Na will play Spain's Azahara Munoz, the NCAA champion from Arizona State; and Whitney Neuhauser of Barboursville, Va., will face Spain's Belen Mozo.

In the third round, Munoz beat Tracy Nichols of Rocklin, Calif., 1-up; Neuhauser, edged Stephanie Kono of Honolulu 1-up, and Mozo routed Canada's Stephanie Sherlock 6 and 5.

Na was 1-down with three to play against the 17-year-old Wong. Na tied it with a birdie on No. 16, then took the lead when Wong three-putted for bogey on No. 17. Wong just missed a birdie putt on 18, and Na tapped in a 3-footer for par for the victory.

"Relieved. Very relieved," Na said. "I'm really happy with myself that I could come back in the end."

Munoz was 2-down after 14 holes against Nichols, but Nichols bogeyed 15 and 16. Munoz birdied the 17th to take the lead. Her 7-foot par putt then caught the right lip of the hole before falling at 18. "It barely went in," Munoz said.

Munoz, Mozo and Ciganda traveled together from Madrid and they're staying with the same host family in Eugene.

"They are like two of my best friends, and it's really cool that the three of us qualified for the quarters," Munoz said.

At 15, Lee is the youngest player left.

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