Only 15 players in the 81-man field had completed the second round at the Fox Chapel Golf Club when rain forced an end to the day's action.
An inch of rain fell on the course in just 15 minutes, leaving the layout unplayable. The opening round was completed Thursday despite a 5-hour rain delay.
Couples was 11-under-par for the tournament after playing 11 holes Friday. First-round leader John Huston was 4-under for the second round through 15 holes and was at 9-under for the tournament.
Shortly before the round was stopped, Huston holed his second shot at the par-4 15th hole for an eagle that brought him within two strokes of Couples.
Jeff Hart was the only one of the front runners to complete his round. He shot a 65 for a 7-under 133 total. Duffy Waldorf was also at 7-under with four holes to play.
Couples is trying to win his second major title on the Champions Tour in as many years. He captured the British Senior Open crown last season. This is the third major event on the circuit this year with two more to come.