The 200 protesters, out of a crowd of 10,000, chanted "death to Saudi," objecting to the role of Saudi armed forces in the bloody crackdown by the Bahraini monarchy on its Shiite subjects over the past months.
Iran's Piroozi team, meanwhile, won the match 3-2, with two goals by Hamid Reza Ali Asgari, in the 13th and 68th minute and one by Shpejtim Arifi in the 16th minute.
Al-Ittihad's Mohammed al-Rashid and Sekou Berthe scored in the 19th minute and during injury time in the second half, respectively.
The game was part of the Group C competition of the Asia Champions League, but also took place between two regional powerhouses on either side of the Middle East's deep Sunni-Shiite divide.
An eyewitness told The Associated Press that two protesters were seriously injured. The Fars News Agency added that several protesters were detained.
Police expelled the protesters from the match in the middle of the second half.
The unrest in Bahrain, which erupted in February, has played out against the region's deep rivalries between Shiite and Sunni Muslims. Protesters from Bahrain's Shiite majority have demanded that the kingdom's Sunni minority rulers grant them equal rights and a political voice.
Saudi Arabia, a largely Sunni nation, has rushed to the aid of Bahrain, while other Gulf countries have accused predominantly Shiite Iran of meddling in Bahrain's affairs by allegedly trying to stir Shiite unrest there.
