Ken Flach and Robert Seguso defeated Andres Gomez and Ricardo Ycaza, 6-2, 6-4, 2-6, 6-4, today to give the United States a 2-1 lead over Ecuador in their best-of-five Davis Cup tennis competition.

Earlier, 18-year-old Aaron Krickstein completed a straight-set victory over Raul Viver, 8-6, 6-1, 6-3. Their match had been interrupted by darkness Friday with the third set tied, 2-2.

Krickstein quickly polished off his opponent when play resumed and tied the series at 1-1.

Gomez won the opening singles match Friday, beating Jimmy Arias, 7-5, 4-6, 4-6, 9-7, 6-4, in a 4 1/2-hour match. Gomez will meet Krickstein in the first of Sunday's reverse singles.

Flach and Seguso needed 2 1/2 hours on the red clay courts to win the doubles before a crowd of 3,000 that half filled Francisco Cano stadium.

The U.S. team got some help as Ycaza made several unforced errors. Seguso and Flach played with confidence and only wavered in the third set, when the Ecuadorans staged a brief rally to the enthusiastic applause of the crowd.

The winning team advances to the quarterfinal round of the World Group to meet the winner of the Mexico-West Germany series.

In that series, Mexico took a 2-1 lead over West Germany when Fernando Perez Pascal and Leonardo Lavalle beat Boris Becker and Andreas Maurer, 3-6, 6-1, 7-5, 3-6, 6-4, in a three-hour 20-minute match at Mexico City's German Club before 10,000 spectators. Becker, ranked fifth in the world, lost his service in the sixth and 10th games of the fifth set.

In Copenhagen, Mats Wilander and Anders Jarryd beat Denmark's Peter Bastiansen and Michael Mortensen, 6-3, 6-3, 6-4, to give Sweden, the defending Davis Cup champion, an insurmountable 3-0 lead in first-round World Group play.

Elsewhere, Roberto Saad and Eduardo Bengoechea beat Uruguay's Diego Perez and Jose Damiani, 9-7, 9-7, 6-3, to give Argentina a 3-0 lead in their second-round match in Buenos Aires; in Santiago, Chile, Hans Gildemeister and Ricardo Acuna defeated Canadians Glenn Michibata and Mark Greenan, 6-4, 3-6, 6-4, 4-6, 6-1, for a 2-1 lead; John Lloyd and Colin Dowdeswell cruised past visiting Spaniards Sergio Casal and Emilio Sanchez, 6-4, 6-3, 6-3, in a World Group match, putting Britain into the quarterfinals for the first time since 1981.