With victories by Gene Mayer and John McEnroe in reverse singles, the defending champion U.S. team completed a 5-0 rout of host Australia in the Davis Cup semifinal in Perth. The U.S. clinched the victory Saturday.

Mayer beat Mark Edmondson, who replaced the injured Peter McNamara, 6-3, 6-3, while McEnroe had a marginally more difficult time against John Alexander, winning, 6-4, 6-3. The matches had been reduced to best of three sets instead of the usual best of five.

The United States will meet France in the final, in Grenoble next month. The French reached the final for the first time in 49 years when Yannick Noah beat Russell Simpson of New Zealand, 6-2, 6-2, 6-2, in the decisive match in Aix-en-Provence . . .

Wimbledon and U.S. Open champion Jimmy Connors defeated Bjorn Borg, 6-4, 6-3, in a $250,000 tournament in Montreal. Connors broke Borg's serve twice in each set . . .

In Philadelphia, Barbara Potter was strong both at the net and the base line in defeating Pam Shriver, 6-4, 6-2, to win the $125,000 U.S. Women's Indoor championship. Potter, whose $22,000 first prize increased her 1982 earnings to more than $210,000, took charge from the opening game when she broke Shriver's serve and coasted through the 65-minute match.