Conversation so far:
When did Pancho Gonzales play open tennis
Gonzales was therefore ineligible to compete at the Grand Slam events between the end of 1949 (when he turned pro) and the start of the open era in April 1968.
What happened in 1968 in tennis for players like Pancho Gonzales?
start of the open era of tennis
why was Pancho Gonzales ineligible to compete in grand slam events prior to 1968?
Before 1968, only amateurs were allowed to compete in Grand Slam tournaments and other events organized or sanctioned by the ILTF, including the Davis Cup.
What happened after the start of the open era of tennis for Pancho Gonzales?
In May 1968, he was the first professional to lose to an amateur

Question: who did he lose to
Self-contained rewrite: Who did Pancho Gonzales lose to when he was the first professional to lose to an amateur in May 1968?