The kind of melodrama that marks a major tennis tournament for greatness came to the U.S. Open today. It arrived in stunning fashion as second-seeded Andrea Jaeger was beaten by Andrea Leand, a 17-year-old amateur from Brooklandville in Baltimore County playing for the first time in the main draw of a professional tournament.

Leand, down 5-2 and 30-0 in the second set, rallied with an array of forehand and backhand drives to shock Jaeger, 1-6, 7-5, 6-3. Jaeger was infuriated by several line calls, the last when she was serving at 3-3, 30-40 in the final set.

As she left the court, Jaeger burst into tears when approached by Lee Jackson, the Women's Tennis Association touring referee. "She missed every call," Jaeger sobbed. "She had three chances and she missed every one."

Jackson, glancing nervously at nearby reporters, hissed, "Not now, Andrea, there's nothing I can do about it."

There was little Jaeger could do with the shots hit at her during the final two sets. "I let her get back in the match," Jaeger said, still red-eyed 30 minutes after the final point. "She didn't have a lot of weaknesses and once she got going she played very well."

The crucial point in the third set was the break point at 3-all. Jaeger had rallied from 0-40 and when Leand looped a moonball return the crowd moaned, apparently thinking the ball would land out. It was close and Jaeger barely returned it. Leand closed in and crunched a forehand winner.

"Oh come ON!" screamed Jaeger, who has a reputation as one of the most even-tempered players in tennis. "You know that was out." She appealed the call to no avail and stalked to her chair, furious.

That call seemed to drain the competitiveness from Jaeger. Mumbling to herself, obviously distraught, she won only two points in the last two games. The final point was a forehand down the line that Jaeger barely touched.

"When I got to match point I was thinking that a lot of people get close to winning against seeded players and then don't finish them off," said the unseeded Leand, who will begin her freshman year at Princeton in 10 days.

Leand's victory broke the tournament out of four days of hum-drum victories by seeded players that continued today. Chris Evert Lloyd strolled to a 6-0, 6-1 victory over Kate Latham, third-seeded Tracy Austin routed Betsy Nagelsen, 6-3, 6-0, and fifth-seed Hana Mandlikova took out Candy Reynolds, 6-4, 6-4.

The top men also had little trouble. Bjorn Borg (2), Jimmy Connors (No. 4), Guillermo Vilas (No. 6), and Gene Mayer (No. 7) won in straight sets, Roscoe Tanner (No. 9), Peter McNamara (No. 11) and Yannick Noah won in four. Only Jose-Luis Clerc (No. 5) had to struggle, needing a 7-3 fifth-set tie breaker to beat Tim Wilkison.

But all else paled in light of the Jaeger upset. It was labeled one of the biggest in Open history, largely because of Leand's lack of professional experience. Her only victory over a pro before today was in the first round over Renee Richards Tuesday.