De Rossi, who spent his entire career in the Italian capital, told fans before the game he had come to Argentina not for the money, although he will doubtlessly be well paid, but for the romance of turning out for one of the world's most storied teams.
"I've been passionate about this club since I was little," the 36-year old said. "This club allows me to play at an excellent level and in the way I enjoy."
In the money-driven world of modern soccer, De Rossi's arrival is unusual in that he has no links to the Buenos Aires club, other than a friendship with their sporting director, his former Roma team mate Nicolas Burdisso.
Most top players who join Brazilian and Argentine clubs at the end of their careers are returning home.
In recent weeks, Dani Alves left Paris St-Germain for Sao Paulo, while Flamengo signed full backs Rafinha from Bayern Munich and Filipe Luis from Atletico Madrid.
But in what could be a new trend, in addition to De Rossi, Spanish defender Juanfran also joined Sao Paulo, prompting the question of whether a trickle of Europeans crossing the Atlantic could grow into something more substantial.
In explaining their reasons for coming to South America, both De Rossi and Juanfran underlined the attraction of playing in front of South America's famously passionate fans.
Both players also highlighted the draw of the Copa Libertadores, South America's equivalent of the Champions League.
The tournament has come under fire in recent years, with the second leg of last year's final moved to Madrid after Argentine police deemed the game too dangerous for Buenos Aires.
That unbridled passion may have helped convince the Europeans to come and experience soccer on the other side of the world.
"Sao Paulo is a Libertadores team," Juanfran said.
"The fans go to the stadium for that competition. Just like at Atletico, there is a culture here to fight for every ball and never give up. We'll be going for it."
Another reason is that although top clubs in South America cannot match the salaries paid by their counterparts in Europe, they can still pay big wages and provide highly competitive standards – as well as offer longer contracts than many teams are willing to give to players in their mid-30s.
For De Rossi, who has been welcomed by fans in Buenos Aires - as well as by former Boca great Diego Maradona - the money is clearly secondary.
"The fact that I am a European player prompts passion and curiosity," De Rossi said.
"I am delighted by that and I hope many more of my colleagues can come from Europe or Italy and experience this love."
"What is the next dream? Winning a big tournament here, that would really be the crowning achievement of my career."