"Syriza has been successful because of the economic crisis - but also because it is the only party that has managed to connect with what is happening in society," said 32-year-old Manos Avgeridis.
He was among hundreds of supporters packed into a tent plastered with banners and flags - many carrying the party's motto "Hope is on its way".
"It's nice there is a party that wants to change the situation because there was no hope," Katia Zagoritou, 34, told me as the radical leftist party's victory unfolded.
"We hope these results can change things also in Italy," added Claudia, 24, who was among hundreds of Italians to fly to the Greek capital for the celebrations.
The word "hope" must be one of the most commonly used around here in past 24 hours.
It was this message of "optimism and dignity" that connected with voters, said Mr Avgeridis.
He has supported the party for a decade, and watched Syriza's share of the vote grow from 5.6% in the 2007 election to 36% this weekend.
Many of those celebrating the latest results began supporting the party - whose name is a Greek acronym for The Coalition of the Radical Left - after the crisis that followed the police shooting of a 15-year-old boy in 2008.
The killing happened just streets away from the campaign tent where the party was celebrating its victory on Monday, in Athen's Exarcheia area. The shooting eventually led to riots by the city's young and poor.
As the election results came in, Syriza supporters find themselves at the heart of the political establishment.
They cheered, sang and hugged in Klafthmonos Square, which has long played a role in Greece's political history. The square's name comes from the ancient Greek word for "crying", after a tradition that lasted until early in the 20th Century of public servants in tears begging a new regime to have their jobs back.
But there were only tears of joy on Sunday night as some supporters danced until the temporary floorboards bounced - cigarette in one hand and can of beer in the other.
"First we take Greece, then we take Berlin," said Anastasia Giamali, 28, who works for the party's campaign newspaper.
The celebrations felt as much European as they did Greek, with loudspeakers blaring a selection of French, British and Spanish music.
Along with the Italian contingent, there were German supporters in the crowd who at one point joined their fellow Europeans on the stage at the front of the party tent.
"This is not only a victory for Greece but for people of Europe. It shows there is an alternative," said one 24-year-old activist from Potsdam.
Moment in history
Syriza supporters hope this victory could bring an end to painful austerity measures that have brought deep cuts to pensions, pay and jobs since the eurozone crisis broke out.
The party's leader, Alexis Tsipras, has vowed to renegotiate the country's bailout agreement with the EU and IMF and boost public spending.
And it is no surprise that so many celebrating are younger voters - unemployment in Greece is 25%, with the figure rising to 50% for those under 25. The average wage is €600 (£450) a month.
There is a feeling among many here that this is a historic moment, and supporters speak in terms of big ideas and dreams.
"For me, becoming an MP is not so important," said Yiannis Giannopoulos, who stood in the second district of Athens aged 28.
"The important thing is the collective vibe.
"We have one chance and we have to take it - not only for Greek society but for the people of Europe that look up to us."
These are grand promises of change. But leave Klafthmonos Square and the plaza outside Athens University where Mr Tsipras made his victory speech, and the streets are much the same as they were before.
Greeks woke up on Monday with their country still in debt by up to 175% of GDP. Their country has still borrowed 240bn euros (£188bn) from the EU, the ECB and the IMF and still needs to find its way around securing the crucial next instalment.
Many Greeks are not feeling so optimistic about Syriza's victory, amid fears that its policies will set the country on a collision course with creditors. Such fears may only grow after the party formed a ruling coalition with the anti-austerity Greek Independents.
But far-left supporters are looking forward to what they hope will be a better future.
"I won't let myself be happy yet," said Katarina Voulalika, a 32-year-old teacher and mother. "I know that just by voting - and putting a particular person in control - nothing really changes.
"I will only be happy when I see a better day for my family. I hope it one day will happen."