In a repeat of the Beijing 2008 Games final, five-time Paralympic champions Iran again came out on top, although they did not have it all their own way at London's ExCeL.
Both teams had won their first three games of the group stages without dropping a set and it was Bosnia and Herzegovina, the world's number two ranked side, who took the first set of their Pool B encounter 25-22.
But this served as a wake-up call for the world number ones, who went on to win the next three sets 25-18 25-18 25-22 - with Ramezan Salehi Hajikolaei at the centre of Iran's best plays.
'We lost our first set although we had a good comeback,' said Iran's Reza Peidayesh. 'In the second set we had to change our tactics. We focused on their strongest point, the spiking, and so we upgraded our block. This is what made us win.'
Germany's men have been the other dominant nation in the group stages and they completed a clean sweep of victories in Pool A with a 3-1 win over Egypt.
After the Germans comfortably took the first set 25-16, the match was a lot closer in the next three sets and despite falling 2-0 down after losing the next 25-22, Egypt got on the board and took the game into a fourth set by taking the next 25-23.
But the Germans, who are ranked number eight in the world, edged another tight set 26-24 to seal victory.
Heiko Wiesenthal, who was one of Germany's standout players in the match, said: 'We are still unbeaten and we are relieved to avoid Bosnia and Iran. If we get through the next match we have two chances at a medal.'
Brazil and China were both assured of a place in the quarter-finals going into their match and were playing off to try and gain a better ranking going into the knock-out stages.
With Anderson Ribas scoring well, it was an ace from Giovani de Freitas that sealed a 3-0 (25-17 25-23 25-20) victory and the South Americans will now face Russia, who comfortably saw off winless Morocco 3-0 in their final Pool A match.
The Chinese now face Germany in the last eight, while Iran take on Great Britain and Egypt go up against Bosnia and Herzegovina.