Qatar's Mendes wants improvement after slow start to World Cup qualifiers
Sardar Azmoun and Mohamed Mohebbi both scored twice as Iran fought back from Almoez Ali's strike into the roof of the net to maintain their challenge for a sixth World Cup appearance.
The loss leaves the Qataris on four points from four games, six adrift of Iran and Uzbekistan, who currently occupy the two automatic qualifying spots in Group A, and at risk of missing out once again on a place at the finals.
"It was a tough game but we know the Iranians are very strong, they have very good players (who are) at a high level," said Brazil-born defender Mendes, who set up Ali for the opener in the 17th minute.
"It's a bad start from us but still we have six games. We need to change our level. Many mistakes, we need to improve."
Qatar have never qualified for the World Cup, only securing their place at the 2022 tournament as hosts, and the closest the nation has come to progressing through the preliminaries was ahead of France 1998 when they lost out to Saudi Arabia.
The top two finishers in each of Asia's three qualifying groups advance to the World Cup while the third and fourth-placed nations progress to a further round of preliminaries.
Qatar are fourth in Group A, level on four points with the third-placed United Arab Emirates and one point ahead of Kyrgyzstan who are fifth. They next host Uzbekistan on November 14th.
Tuesday's game was a rematch of the Asian Cup semi-final in February that Qatar won on the way to a second successive title and when Ali smashed the ball home Tintin Marquez's side looked to be on the path to a similar result.
But Azmoun headed in the equaliser three minutes before the break and then put his side ahead in the 48th following a mix up between Mendes and goalkeeper Meshaal Barsham.
Azmoun set up the third in the 65th minute for Mohebi, who then wrapped up the win deep into added time as the Iranians avenged their loss at the continental championship.
"It was a really important three points," said Azmoun. "Really, it was a really easy game for us. We didn't expect that the game would go like that."