Alice Chen entered her sophomore tennis season at Quince Orchard High School intent on improving her performance from last year, when she advanced to the Montgomery County and regional tournaments and earned a berth in the state championships. She cruised through the regular season undefeated before encountering Monica Mackova, a foreign exchange student at Paint Branch.

Mackova snapped Chen's unbeaten streak in the semifinals of the county tournament. The native of the Czech Republic went on to reach the finals of the Region II tournament and earn a berth as one of the county's two girls' singles players in the state tournament, which begins today at the University of Maryland.

Mackova has gotten plenty of support from Paint Branch's administrators and coaches, as well as from teammates who have taken a lesser role on the team than they anticipated before the season. So has Derek Ralet, an exchange student from Belgium who will represent Old Mill at the state tournament.

But for all the positive aspects area tennis coaches and officials see exchange students bringing to school teams, they acknowledge another side -- that these players often beat Americans, and in the process take away trophies, state and regional berths and spots on the team. The issue has drawn particular attention in Maryland this year, as Mackova and Ralet have progressed toward the state tournament.

"It's kind of every year, you wonder who has the exchange student," said Severna Park boys' tennis coach April Pinder, whose junior, Matt Bulkley, suffered all four of his losses this season to Ralet. "You do feel for Matt, who's looking at his shots dwindle. It is unfortunate. But I've had exchange students in the past, and I think it enriches everyone."

Ralet went undefeated in the regular season, captured the county championship and the Region V title. Two years ago, Jake Benzel, a foreign exchange student from Spain who attended Franklin High School in Baltimore County, won the boys' singles title at the state championship.

State rules allow for foreign exchange students to participate in extracurricular activities while attending school, as long as they meet the same eligibility standards other students face.

"We treat them just like any other student in school," said Gaby von Nordheim, a Montgomery County athletic official who also serves as state tournament director. "It's sort of the luck of the draw. . . . Like this year, we have Monica and Derek. Some years, we don't have any."

But von Nordheim -- who has hosted exchange students in the past -- knows that tensions can arise when resident student-athletes -- particularly seniors -- are displaced by foreign exchange students.

"If you've been on a team and you're a senior and you get bumped because of an exchange student, then that can be disappointing," she said. "Everything has its plusses and minuses, depending on whether you use it as an experience to grow or improve upon or just think it isn't fair."

It's not uncommon for transfer students to excel at tennis -- in large part because the national tennis federations in many European countries heavily subsidize youth programs.

Paint Branch junior Kathrina Aben said she was initially disappointed when she was replaced at No. 1 singles by Mackova after losing in a challenge match in tryouts. But she said she quickly understood that Mackova's addition was better for the team because it provided more depth.

Aben moved to No. 2 singles, where she finished with a 13-1 regular season record that helped lift Paint Branch to an 8-5 record, good enough for third in Division II. A year earlier, Paint Branch finished seventh out of eight teams in the division.

"Players have their pride, and of course I wanted to be the number one singles player," said Aben, who qualified to compete in mixed doubles in the state tournament with partner Eric Sundstrom. "But the team did better with Monica playing there. I got over it after a week. . . . It was great having somebody of her caliber to hit with. You only get better playing with stronger competition."

Quince Orchard's Chen said she was more frustrated by the fact that she did not meet her own expectations than by Mackova's emergence from nowhere to become one of the county's top players.

"I was hoping that I could do a lot better this year, but I didn't," said Chen, who is ranked 14th among 16-and-under girls in the USTA's Mid-Atlantic region. "I still have next year, so it's not a lost opportunity."

Mackova had not competed seriously in tennis since she was 15, when she began experiencing back and knee pain after a sudden growth spurt. But the 17-year-old amassed a 16-3 overall record for Paint Branch this season, with all of her losses coming against two-time county and region champion Maggie MacKeever of Churchill.

At the state tournament, Mackova knows she will likely have to beat Glenelg senior and top seed Julia Facchina, who finished third last year, to advance to the finals.

"I just wanted to do something while I was here. If I didn't, I would have been lazy," Mackova said. "I didn't know what to expect when I came here. I've had so much fun. I just want to try and do my best. I can't do anymore than that."

Old Mill's Ralet wanted to come to the United States to improve his English and get a chance to play competitive tennis. Ralet's arrival could not have come at a better time for the tennis program at the Millersville school, where the No. 1 singles player had quit the team for personal reasons, Coach Krissy Dryden said.

Ralet seized the opportunity by winning 18 consecutive matches without dropping a set. Although he will return to Belgium this summer, he said he hopes to return to the United States and attend college, perhaps on a tennis scholarship.

"I learned too late about scholarships and didn't apply anywhere," Ralet said. "I wanted a country where I could learn English. When I knew I could play tennis because high schools have teams, I said, 'I'm going to the USA to play tennis.' "

But he, too, faces a tough draw in the states, where he would need to defeat defending state champion and two-time All-Met Michael Goodwin to advance to the final.

Severna Park's Bulkley has taken his losses to Ralet in stride, even though the defeats kept him from defending his region title; his school finished second to Old Mill in the county championship.

"As much as I want to win counties and regions, it wouldn't mean as much if it wasn't over someone who was a challenge," Bulkley said. "Derek is such a quality player and classy guy that you can't hate him. He'll beat you, shake your hand and offer you a drink of water."

Derek Ralet, a student at Old Mill from Belgium, is undefeated and vying for Maryland state title. Two years ago, a Spaniard won the boys' title at states.