When Eric Korita entered Southern Methodist University, he was dubbed "Orca," a backhanded compliment to being 6-foot-5 and 240 pounds. He ate six meals a day and there was hardly a dish he disliked.

"Calling him fat would be an understatement," said Dennis Ralston, his coach at SMU and a former captain of the U.S. Davis Cup team. "Getting rid of the weight was his main problem. Once he did that, he found he could move better."

He's 40 pounds slimmer now, the only amateur in the quarterfinals of the $200,000 D.C. National Bank Classic, and, according to many observers, should be a whale of a tennis player.

"He's got potential to be top 10," said Ralston.

Korita turned quite a few heads in the sweltering heat--reportedly 105 degrees on the court--Thursday by serving 12 aces in a 6-3, 4-6, 7-5 upset over eighth-seeded Fernando Luna. He will play Francesco Cancellotti of Italy today.

Korita's 120 mph serve has been the talk of the tournament.

"Best serve in the world," said Luna, ranked 64th in the world, after what Korita said was his biggest victory on his whirlwind summer tour.

"I'm not enjoying watching Eric serve," said Jimmy Arias, former teammate at Nick Bollettieri's tennis academy in Bradenton, Fla.

Korita learned the serve from Nick Barone, the pro at Fullerton Tennis Club in Chicago, the same pro who gave Korita's father lessons when 9-year-old Eric asked to join in.

"I hit some balls, then took some lessons and found I was pretty good at it. Nick taught me my serve. He really taught me well."

Korita grew up in the Chicago suburb of Glenview, where he played both basketball and tennis before tennis won out, although Korita did play basketball at Glenbrook South High School for two years. In his junior year, he left home for Bollettieri's school.

In Florida, Korita practiced against future pros Arias and Mike DePalmer for four hours a day. School was in the morning from 8 to 12:30. He planned to go for six months; he stayed two years.

"I've worked with him for five years now," said Bollettieri, "(He's) nice and humble. He just needs to be more tenacious on the court. He needs more muscle tone now that he's slimmed down a lot."

Korita attracted the attention of SMU's Ralston, who felt the dynamic serve, the big forehand and "adequate backhand" showed potential, despite Korita's weight problem.

"I always had a big appetite as a kid," Korita said. "I cut down from six meals a day to three. I never had a real schedule of eating. I have a problem: I like everything.

"But then I changed my habits, cutting down on everything I ate, the types of things I ate. Started working out more."

Korita jumps rope and does wind sprints to improve his quickness. Last year he dropped 40 pounds before the U.S. Open and advanced into the third round, playing Yannick Noah on center court.

"Before I went out for that match I was nervous. The place was so big, there were so many people there. center court was overwhelming at first. I thought I had the opportunity to win," he said of the five-set loss. "(I) probably lost because of a lack of experience and was a little unlucky at times."

Korita, a prebusiness major, will be taking off the fall semester at SMU. "If I do well, it wouldn't make sense (to return)," said Korita.

Korita, who says he's not nervous about playing in the quarterfinals here, probably gets some of his self-confidence from his ability to sing in front of crowds. Two years ago, at an end-of-the-year party at Ralston's house, Korita plugged a Mr. Microphone into the tape deck and sang along with the tunes for almost two hours.

"He sings a lot on the road," Ralston said. "Sings along with his Walkman. Actually he has a pretty good voice. He can carry a tune."