While numbers are disputed, the fact that people dared to turn out on the streets of Tehran and elsewhere to protest is a victory for the Iranian opposition movement brutally quelled in 2009.
Opposition in Iran proves it is still strong
Galvanised by the uprisings in Egypt and Tunisia, Iran's opposition broke through the barrier of fear.
Risking cracked skulls, arrest and long jail terms, they took to the streets in significant numbers for the first time in a year to prove that the Iranian opposition is resilient and strong.
The regime had written off the "green" movement as a "corpse". Now Iran is the first non-Arab country to be affected by the political contagion gripping parts of the Middle East.
Monday's pro-democracy protests in Tehran and several other cities, organised mostly through Facebook, were as embarrassing for the Iranian authorities as they were a morale boost for the opposition.
There was a predictably furious response from hardline factions in Iran yesterday. A majority of lawmakers in parliament called for the death penalty for opposition leaders they accused of fomenting Monday's protests in which at least one person was killed and dozens wounded. State television called protesters "monarchists, thugs and seditionists".
The government, in turn, has been accused at home and abroad of hypocrisy for gleefully championing the revolution against an "American puppet" in Egypt while declaring that similar rallies in Iran would not be tolerated.
Even the protest destinations had an uncomfortable resonance for the Iranian government. Demonstrators headed to Tehran's Azadi, or Freedom, Square; Egyptian protesters operated out of Cairo's Tahrir, or Liberation, Square.
"The Green Wave proved that it could still surge," declared Enduring America, a blog with expert Iran coverage. Monday's protests, it added, were the biggest victory for the opposition since the last mass protests in December 2009, when eight people were killed.
Many protesters went unmasked, while plainclothes regime vigilantes covered their faces to avoid identification, a witness to Monday's events said in an interview.
More anti-government protests are expected in coming days, he added.
The Iranian opposition has frequently challenged the government to a show of strength, insisting its supporters would easily outnumber the regime's in rival rallies if they were allowed to take to the streets without fear of violence or arrest. The government has refused to take up the challenge.
Inevitably, Iranian officials are blaming foreign powers for the turmoil, insisting only a few hundred had taken to the streets; independent witnesses put the figure in the tens of thousands.
The numbers dispute misses the point. That any dared protest was remarkable given the harsh response of authorities to the six months of unrest after President Mahmoud Ahmadinejad's disputed re-election in June 2009. Scores were killed and dozens jailed following mass show trials.
Iran's deputy police chief, Ahmad Reza Radan, claimed yesterday that the protests had been directed by "America, England and Israel".
Kayhan, a hardline daily newspaper close to the supreme leader, Ayatollah Ali Khamenei, branded the protesters "scum".
Mr Ahmadinejad was the focus of most slogans in the previous mass demonstrations that shook the regime. But on Monday, the chants were also directed at Ayatollah Khamenei. "Mubarak, Ben Ali, now the turn of Sayed Ali," some protesters jeered, referring to the deposed dictators of Egypt, Tunisia and their own supreme leader.
Analysts in Tehran said the mood is now buoyant among opposition supporters who had been asking themselves: "Why have Tunisians and Egyptians made it, but we did not?"
There are several answers. The Iranian regime has a firm grip on the levers of repression and can rely on volunteers in the Revolutionary Guards and its affiliated Basij paramilitary force to crush dissent.
Both are ideologically driven and have vested financial interest in protecting the regime, which has generously rewarded their stalwart loyalty.
Trita Parsi, president of the Washington-based National Iranian American Council, said either Mr Mubarak nor Mr Ben Ali had a "massive force with an ideological commitment to the regime that is willing to use brutal violence against the civilian population over a prolonged period."
In addition, Tunisian and Egyptian protesters coalesced around the single goal of ousting leaders, he said. The Iranian opposition, in contrast, does not have a cohesive goal. Its old guard, led by Mir-Hossein Mousavi and Mehdi Karrubi, were once pillars of the Islamic revolution. They want the system reformed, not overthrown.
The anti-Khamenei chants of some younger protesters on Monday suggest more radical aims.
The Iranian government also faces growing pressure abroad. Monday's protests were directly encouraged by the US for the first time. Hillary Clinton, the secretary of state, hailed the "courage" and "aspirations" of the protesters and urged Iran to follow Egypt's example and "open up".
Washington had previously held back from directly endorsing the opposition out of fear that US support would backfire on protesters.
Britain, meanwhile, is talking to other countries about ratcheting up the pressure on Iran over its nuclear programme. That could mean tightening already tough sanctions or imposing additional ones.
The Iranian government is already feeling vulnerable on the economic front. It is struggling to cope with rising prices and unemployment, factors that helped drive the uprisings in Egypt and Tunisia.
But while some Arab governments have been rushing to increase subsidies to head off unrest, Iran has been phasing them out. Petrol prices in Iran have surged seven-fold in the past two months.
Robert Powell, an analyst at the Economist Intelligence Unit in New York, said: "The economic fallout from the recent subsidy reductions has yet to be fully felt by the population. Arguably, it is this rather than the revolt in North Africa that could precipitate any future mass protests."