The International Tennis Federation is giving Olympics players extra time during breaks in play after facing criticism for staging matches during the highest heat of the day.
The federation says change of ends and set breaks have been extended by an extra 30 seconds and will now be one minute, 30 seconds.
Temperatures have risen above 86 degrees F (30 degrees C) for a second straight day at Ariake Tennis Park.
Second-seeded Daniil Medvedev had asked for longer breaks to bring the Olympics into line with regular tour events. The federation says it will consider suspending play if temperatures keep rising.
Top-seeded Novak Djokovic and Medvedev both questioned why matches Saturday were not moved into an evening session.