The retirees gather each week to protest cuts to their pensions, which have dried up since libertarian President Javier Milei took office in late 2023.

But the unexpected support on Wednesday comes after previous protests ended with several injured elderly.

One white-haired woman held up a shirt that read, "Don't hit us, we are your parents!"

Behind her stood supporters of Boca Juniors and Racing - two of Argentina's "Big Five" teams - as well as fans of local team Chacarita Juniors, who first launched the call to show up on Wednesday for the retirees' weekly protest.

The soccer fans adopted a phrase from Argentine great Diego Maradona in their march - "How could I not defend retirees? You'd have to be a real coward to not defend retirees."

Milei has slashed pension payouts as part of a government spending overhaul meant to tamp down on rampant inflation.

But that has some at the detriment to Argentina's most vulnerable, the opposition alleges.

"We're in favor of cleaning up public finances," center-left Senator Martin Lousteau said in a post on X. "What we can't let happen is for these fixes to happen on the anguish, health and abandonment of our retirees."

Wednesday's protest also ended in violence, with Security Minister Patricia Bullrich warning the so-called "barras bravas" that there would be law and order.

Police used water cannons and rubber bullets to disperse the thousands of protestors outside of Congress after some were seen throwing rocks and other objects.

Authorities said nearly 90 people had been detained and 15 people had been taken to hospital, among them a police officer who had been shot and a protestor who had been hit in the head with a tear-gas canister.