Άνοιξαν τη σαμπάνια χτες.

Άνοιξαν is the 3rd person plural aorist form of ανοίγω (to open).

So it means they opened.

A few useful details:

• ανοίγω = I open / to open
• άνοιξα = I opened
• άνοιξαν = they opened

The aorist is the usual Greek past tense for a single completed action. In this sentence, it presents the opening as a finished event.

Greek often drops subject pronouns when they are not needed.

So instead of saying:

• Αυτοί άνοιξαν τη σαμπάνια χτες. = They opened the champagne yesterday.

Greek normally just says:

• Άνοιξαν τη σαμπάνια χτες.

The ending -αν in άνοιξαν already tells you the subject is they, so αυτοί is usually unnecessary unless you want emphasis or contrast.

Because σαμπάνια here is the direct object, and Greek commonly uses the definite article where English would say the.

So:

• η σαμπάνια = the champagne (subject form / nominative)
• τη(ν) σαμπάνια = the champagne (object form / accusative)

Since the champagne is what they opened, it has to be in the accusative:

• Άνοιξαν τη σαμπάνια. = They opened the champagne.

Τη is a very common shortened form of την before a consonant.

Both are used:

• την σαμπάνια
• τη σαμπάνια

In everyday speech and writing, τη σαμπάνια is completely normal.

A useful rule of thumb:

• Before a vowel or certain consonant clusters, you are more likely to see την
• Before many consonants, τη is very common in modern usage

So this sentence sounds natural as written.

It is in the accusative singular, because it is the direct object of the verb.

However, with this noun, the nominative and accusative forms look the same:

• η σαμπάνια = nominative
• τη(ν) σαμπάνια = accusative

So the article changes, but the noun itself stays σαμπάνια.

Χτες means yesterday.

Yes, it is essentially the same as χθες. The difference is mostly one of style and spelling:

• χτες = very common in everyday language
• χθες = also correct, sometimes felt as slightly more formal or more conservative in spelling

So:

• Άνοιξαν τη σαμπάνια χτες.
• Άνοιξαν τη σαμπάνια χθες.

Both mean the same thing.

Yes, Greek word order is fairly flexible.

This sentence has a very natural order:

• Άνοιξαν τη σαμπάνια χτες.

But you could also say:

• Χτες άνοιξαν τη σαμπάνια.
• Τη σαμπάνια άνοιξαν χτες.

These all mean basically the same thing, but the emphasis changes slightly:

• Χτες... puts focus on yesterday
• Τη σαμπάνια... puts focus on the champagne
• Άνοιξαν... is the more neutral start

So the original sentence is just one natural way to say it.

Because Greek usually builds tense into the verb itself.

English often uses helping words:

• they did open
• they have opened

Greek does not need a separate auxiliary here:

• Άνοιξαν already means they opened

So one word carries the information for:

• person: they
• tense: past
• aspect: completed action

Here it means a completed action: they opened it.

The aorist is normally used for a whole event viewed as complete.

So Άνοιξαν τη σαμπάνια χτες suggests:

• the opening happened yesterday
• it is seen as a finished event

If you wanted an ongoing or repeated past meaning, Greek would usually use a different form, such as the imperfect:

• Άνοιγαν... = they were opening / they used to open

So άνοιξαν is the right form for a simple completed event.

It is a loanword, ultimately from champagne.

In Greek it has been adapted to Greek spelling and pronunciation:

• σαμπάνια

Like many borrowed nouns in Greek, it behaves like a normal Greek noun and takes Greek articles:

• η σαμπάνια
• τη σαμπάνια

So even though the word is borrowed, its grammar in the sentence is fully Greek.

A simple pronunciation guide would be:

Á-nee-ksan ti sam-BÁ-nya htes

A few helpful points:

• Άνοιξαν: stress on the first syllable
• μπ in σαμπάνια is pronounced like b
• χ in χτες is a rough sound, not like English h, but htes is a rough approximation

So the sentence sounds roughly like:

AH-nee-ksan ti sam-BA-nya htes

Not naturally in this exact form.

Because Greek uses τη σαμπάνια, the sentence refers to a specific champagne / the champagne.

So the most direct translation is:

• They opened the champagne yesterday.

If Greek wanted a more indefinite sense, the wording would usually be different. In this sentence, the article strongly suggests a specific bottle or specific champagne already known from context.