Their long blond hair was drawn into matching braids that trailed down their backs, their faces were twisted into identical stares of concentration, but when Mary Pierce and Anna Kournikova's first-round match at the Chase Championships hit the critical stages at Madison Square Garden tonight, it was Pierce who distinguished herself with mental toughness her 18-year-old opponent could not equal.

Kournikova had been two points from winning the match in the second set when Pierce began to battle back, first slowly, then with more vigor as she pushed the set to a tiebreaker. Faced with the same kind of pressure she had just been shoveling out, Kournikova crumbled, winning just five points over the course of the third set before falling, 6-7 (7-3), 7-6 (7-5), 6-0.

"I didn't have any problems with my game, with playing--it was just mentally that I kind of left the court," Kournikova said. "You try to keep going, but it's tough."

The result was a sharp disappointment for the young Russian, who had been hoping this year's more open field would help her find the success that has eluded her in the past. The $2 million tournament, which features 16 of the top 17 players in the world, has a much different look now that six-time champion Steffi Graf has retired and three-time champion Monica Seles is out with a foot injury.

Four first-time competitors are entered, including Venus and Serena Williams and 23-year-old Austrian Barbara Schett, who did her part to establish the tour's new guard by dispatching Arantxa Sanchez-Vicario, 6-1, 6-4, in tonight's other match.

But while Schett practically cruised to victory, taking advantage of an unprepared Sanchez-Vicario, Kournikova was erratic, at certain points pounding shots past Pierce and at others looking too listless to get the ball back over the net. She certainly opened the match with a lot of energy, going up an early break and then winning the first-set tiebreaker when Pierce hit first a backhand, then a forehand long. And she also looked good at the start of the second set, cruising to a 4-1 lead before piling up two break points on Pierce.

But instead of converting her chances, Kournikova allowed Pierce to work her way back into the match and salvage her service game to cut the score to 4-2. Kournikova continued to fight, winning her service game and forcing the next game to deuce, putting her two points away from winning the match, but again, Pierce battled, winning back the game. Pierce then broke Kournikova at love to get the set back on serve, and when she won the tiebreaker, Kournikova appeared near tears.

She never recovered, allowing Pierce to complete the kind of comeback that has been difficult throughout her career.

"I have had a tough time coming back from when I was down before--I wasn't able to just take a step back and really try to think and analyze what was going on," Pierce said. Tonight, "I just really told myself to just play every point, point-by-point. Just think, concentrate and think about what was going on."

Sanchez-Vicario could complete no such comeback in her match against Schett, looking sluggish from the moment she stepped on the court. Schett took advantage by racking up a 5-0 lead in the first set, although Sanchez-Vicario did begin to show a little more punch in the second set. Finding some of her strokes, Sanchez-Vicario began winning her service games, and even when she didn't, she was able to break Schett back to keep the set tied. Still, by the end of the night, Sanchez-Vicario appeared overmatched, barely managing to hold off one match point before finally succumbing with a long forehand on the next.

"I was expecting to just play doubles here--I was the last one [selected] for the main draw and was probably not at my best," said Sanchez-Vicario, who took the spot vacated by the injured Seles. "The first set went way too fast--all the games went to her side, and I was missing a lot. In the second set, I was starting to get a little more close."

Schett's appearance here rounds out a strong season in which she has reached a career-high ranking of No. 7. While her run may end shortly--she will next face the winner of Wednesday's Venus Williams-Conchita Martinez match--she is thrilled to be part of the new guard at Chase.

"I'm glad [Graf and Seles] are not playing--it's more chances for me," Schett said. "It's great to play here--it's the top 16 players here. And it's a big experience for me because it's the first time I've been here."

Chase Notes: Ticket sales at Madison Square Garden are up 30 percent over last year, with semifinal and final-round sessions nearly sold out. . . . The WTA Tour will wait until Wednesday to announce that Sanex, a subsidiary of Sara Lee, will be its new sponsor.