HILTON HEAD ISLAND, S.C. (AP) -- Martina Hingis understands tennis more now than she did the last time she came to the Family Circle Cup in 1997.

Then she was the youngest No. 1 player in history and filled with a captivating confidence. Today, she's also No. 1, but with a careful appreciation of what it takes to stay there.

No longer does everything come easy for the 18-year-old Hingis, top-seeded at Sea Pines Racquet Club.

Hingis, who topped Sylvia Plischke 6-3, 7-5 in her first match Wednesday, felt unbeatable two years ago and confirmed that with six straight championships and a 37-matching winning streak.

``But you have to sometimes at that stage watch out to keep motivating yourself,'' she said, ``because other players are going to go after you, and that's what (they're) doing now.''

Others who advanced were No. 2 Monica Seles, No. 6 Patty Schnyder, No. 10 Conchita Martinez, No. 13 Silvia Farina, No. 14 Elena Likhovtseva, No. 16 Henrieta Nagyova and unseeded Iva Majoli.

Last year, Hingis learned it wasn't easy to stay on top. She won five times, down from her 12 titles a year earlier, and took only one major, the Australian Open.

By year's end, Lindsay Davenport supplanted Hingis as No. 1 and sisters Venus and Serena Williams began to crowd the spotlight.

``I know how I felt when I kind of played at the top level and nobody was beating me. You just feel invincible,'' said Hingis, sounding more wistful than an 18-year-old megastar should.

Especially one who's back on top after regaining No. 1 with consecutive wins at the Australian and Pan Pacific tournaments in February.

She said moving from the hard surfaces of the Lipton Championships to the slow clay of Sea Pines caused some serious lapses against Plischke.

After taking the first set without much trouble, Hingis fell behind 3-0 in the second. Just as suddenly, she was up 5-3. But she needed four more games to close out Plischke.

``I had kind of relaxed after the first set,'' she said. ``I just should have gone for it more.''

Seles looked sharp in her opening match, winning the final eight games to dump Olga Barabanschiova 6-3, 6-0. Seles had expected to practice more on clay, but that didn't happen when, with Mary Joe Fernandez, she reached the Lipton doubles final before losing to Hingis and Jana Novotna.

``I was hoping after my singles, I'll come here, get ready for clay,'' Seles said. ``But it didn't go as I planned.''

Schnyder defeated Lisa Raymond 6-4, 6-2, while Martinez, who won this tournament in 1994-95, ousted Alexia Dechaume-Balleret.

Martinez now will face Hingis, who would seem to have this tournament to herself with Serena Williams and Davenport out with injuries, and Venus Williams' decision to pass.

But Hingis, who lost in the Lipton semis to Serena Williams, said her game has grown more powerful and polished since 1997 and she is not ready to back down if challenged by the Williamses or anyone else for the top spot.

Hingis, noting that neither sister has yet to win a Grand Slam event, said: ``Once they do this, OK. But not yet.''