Translation:The day started as a classic Sunday.
10.05.2013 O dia começou como um domingo de clássico, assemelhando-se àqueles em que o Vasco da Gama entra em campo para enfrentar rivais de maior porte ou times de menor expressão. Sempre que o Vascão joga, é assim. Os dias parecem outros. São diferenciados, especiais, inigualáveis. Ah, Vasco! Vascão! Vasquinho! O meu, o seu, o nosso Vascão. O time do coração de todos os brasileiros...Domingo de clássico! Português sem jaça! Principalmente quando joga o time da raça!
"Clássico" in this meaning is a traditional match between great popular teams. A "domingo de clássico" is a Sunday when this traditional match occurs. Their fans just think and talk only about that... it's a "Sunday of clássico"... A classic Sunday is a common or regular Sunday...
Well, this is very specific. "Domingo de clássico" is not a classic sunday (whatever that means), but a sunday with an important match (almost always a soccer match) between two important teams. "Clássico" in soccer here in Brazil has this meaning of an important match (like Yankees versus Giants in USA). The "de" is used when you are talking about an event happening that day. For example, I would say "domingo de páscoa" to talk about "easter sunday" and not any common sunday, or "dia de natal" to refer to "christmas day". It is the "de" that tells me this sunday has a special meaning, in this case, a sports event. Of course there is no hint in duolingo about all this, but brazilians will understand immediately. Proof of that is the comment in portuguese of Valdemar Vascaino down here, try to read it ;D
Well, I guess in English classical is more related to music, as in classical music. Maybe a classical Sunday is some hour long Beethoven Special on the radio for the Family? ;D
But a classic Sunday would be that day to be remembered, when something really worth or cool happened. Or even traditional: '- Sunday we are going to play poker all night long' '- Hey, that's a classic!'