The United States, with Ken Flach and Robert Seguso winning the doubles yesterday, took an unbeatable 3-0 lead over Japan in their Davis Cup tennis series at Kyoto.

WCT doubles champions Flach and Seguso put away Shigeyuki Nishio and Shunichi Sakamoto, 6-2, 6-3, 6-1.

The U.S. team, with victories from Eliot Teltscher and Aaron Krickstein in singles matches Friday, can play just for practice in Sunday's reverse singles pairings in the best-of-five elimination.

The United States advances to a second-round series in August against West Germany, which took a 3-0 lead over Spain with a doubles victory in five sets at Sindelfingen.

The U.S. pair never lost service. The match lasted 81 minutes.

Australia's doubles team needed more than four hours to gain a 2-1 first-round World Group lead over Yugoslavia, Pat Cash and John Fitzgerald outlasting Slobodan Zivojinovic and Goran Prpic, 7-5, 10-12, 6-8, 6-4, 6-4, at Split, Yugoslavia.

At Tbilisi, U.S.S.R., the Soviet duo of Alexander Zverev-Sergei Leonyuk cut Czechoslovakia's lead to 2-1 by rallying past Tomas Smid-Libor Pimek, 3-6, 4-6, 11-9, 8-6, 7-5.

Hana Mandlikova, 16 hours after beating Martina Navratilova, defeated Catarina Lindqvist, 6-3, 7-5, for the $150,000 U.S. Women's Indoor championship and $30,000 first prize at Princeton, N.J.

"I think my fighting spirit is much better than it was," said Mandlikova. "If something doesn't work, I don't lose my head but I try my hardest."