MEXICO CITY -- Experience paid off for the U.S. Davis Cup team yesterday afternoon.

Troubled by the 7,250-foot altitude, temperatures near 90 degrees, a festive holiday crowd and his opponent's perfectly executed aggressive game plan, Jim Courier was upset in his Davis Cup debut by Luis Herrera, 6-4, 2-6, 7-5, 6-4.

But in the second singles match of the three-of-five-match first-round series, a veteran, Brad Gilbert, defeated Leonardo Lavalle, 6-3, 6-2, 6-7, 6-3, to avoid a first-day sweep. Jim Pugh and Rick Leach of the United States are scheduled to play Jorge Lozano and Lavalle today, with two more singles matches tomorrow.

"Altitude is the great equalizer," said Courier, 20, a Floridian, who had played his way onto the American team and to the world No. 9 ranking with a two-tournament, 12-match victory streak earlier TTC this month. "I never felt comfortable hitting the ball; I felt I had to hold back on the ball."

Courier had beaten Herrera, 19, last week at the Lipton Players Championships in Key Biscayne, Fla., on his way to the title, but the Mexican had approached this match with confidence because of the drastically different playing conditions.

"This was his first time in Mexico and maybe he had practiced great, but I knew in the match that he was going to miss a lot," said Herrera, who is ranked No. 99 in the world.

In the second match, Gilbert, 29, had an easy time early on, but he appeared to lose his concentration in the third set, and couldn't regain it in the tie-breaker.

In the fourth set, Lavalle, 23, gained a service break to go up, 2-1, but Gilbert broke back immediately for 2-2, then gained the crucial edge when broke the Mexican's service again to take a 4-2 lead.