Unseeded Emilio Sanchez of Spain beat Boris Becker, 6-3, 6-4, yesterday in the quarterfinals of tennis' $435,000 Italian Open. No. 1 seed Ivan Lendl and defending champion Yannick Noah advanced to a semifinal showdown.

Noah overcame a stiff challenge from Uruguay's Diego Perez, 7-6 (7-5), 6-4. Lendl defeated Henri Leconte, 6-4, 6-2, to set up today's date with Noah, who beat him in two sets Saturday in the Tournament of Champions at New York.

Sanchez, ranked 34th in the world, next faces No. 2 seed Mats Wilander, who ousted Libor Pimek, 6-1, 6-2, in the closing quarterfinal on the center clay court of Rome's Foro Italico.

Sanchez, 20, a stocky right-hander, won all his service games against Wimbledon champion Becker. Lendl used forehands and lobs to wear down Leconte, who upset him in the 1985 Wimbledon and only recently recovered from viral hepatitis . . .

On clay in West Berlin, top seed Martina Navratilova overcame Catherine Tanvier, 6-3, 7-6 (7-4), to reach the quarterfinals of the women's $150,000 West German Open. Tanvier had leads of 3-2 in the first set and 4-3 in the second.