U.S. Equestrian Team rider Michael Matz aboard Brussels ensured a U.S. victory in the team competition at the Washington International Horse Show when the 9-year-old gray mare won the $40,000 President's Cup Grand Prix at Capital Centre.

Brussels was the last to go in a six-horse jumpoff and was clocked in a faultless 30.66 seconds. The class began during the afternoon with 39 entries. Only 20 returned for the first evening round, conducted over 14 obstacles including a demanding triple jump and a double set of fences that contained a water jump.

Matz, going last, knew he had to beat the faultless 32.71 clocking set minutes before by Rodney Jenkins aboard The Natural.

"She's a lttle bit tough to ride, but she's getting better," Matz said of the Belgian-bred mare who has a reputation for being inconsistent and hard to handle.

But last night she took each fence perfectly and quickly. "She's careful and I think she'll get better," said Matz. "Actually I was lucky I was clear in the first (afternoon) round. She bounced a rail."

Brussels is owned by the Rex Group Inc. and is on loan to the U.S. team.

Jenkins, of Rapidan, Va., ensured a jumpoff in the first round when The Natural went clean after seven others had faulted out. Jenkins' second-place ride aboard The Natural helped him earn both the show's National Rider award and the U.S. Tobacco rider award.

Matz's ride gave the United States a total of 41 points to 31 for Canada and 28 for West Germany.

Canada's Hugh Graham was the show's best international rider with 11 points and teammate Alexa Bell was runner-up with 10.

International team and open jumping continues Tuesday night at the National Horse Show in New York's Madison Square Garden. In afternoon competition yesterday, rider Jenno Topping, 17, a part-time New York model, was awarded the $10,000 International Junior Rider Scholarship for points scored during the eight-day show.