ROCKVILLE, Md. (AP) — Top-seeded teenager Rachel Heck opened a big lead early and then had to hang on to beat Therese Warner in 18 holes to advance to the second round of the U.S. Women’s Amateur on Thursday.

The Women’s Amateur has not been kind to the medalists, with four of the last six No. 1 seeds losing in the opening round.

Heck, the 18-year-old from Tennessee, won the opening four holes and remained 4 up through 11 holes. Warner won the 12th and 14th, and then made a 50-foot birdie on the 17th to send the match to the final hole at Woodmont Country Club. Heck won, 2 up.

Defending champion Gabriela Ruffels trailed as she neared the turn until winning five of seven holes in a 3-and-2 victory over Rajal Mistry.

Zoe Antoinette Campos, a 17-year-old California, won nine of her 13 holes in a 7-and-5 victory over Pimnipa Panthong, while Kaleigh Telfer of South Africa also had a short match, beating Talia Campbell, 6 and 5.

The second and third rounds are schedule for Friday, followed by quarterfinal and semifinal matches Saturday and the 36-hole championship match Sunday.

“I’ve never made it past the round of 64, so I’m excited to be here,” Heck said. “No matter what round it is, what seed you’re playing, you’re not going to have an easy match. These are the best amateurs in the world.”