Middle blocker Seyed Mohammad Mousavi was dominant for Iran, recording five points off of blocks, as Iran won the battle of the block, eight points to three.
Shahram Mahmoudi led Iran with 17 points, while Americans Matthew Anderson and Aaron Russell both had nine points.
The Iranian team had defeated USA on Friday 3-0 (25-19, 29-27, 25-20) at Azadi stadium.
USA and Iran first met in 2015 the first weekend of World League on May 30-31. USA won both matches, 3-1 at the Galen Center in Los Angeles before large crowds that included many Iranian fans.
USA still leads Pool B with 17 points, while Iran is in third place with 13 points. Iran handed USA its only two loses in Pool B.