ungeschlagen
unbeaten
Not having been defeated in a competition, fight, or game.
Die Mannschaft ist in dieser Saison noch ungeschlagen.
The team is still unbeaten this season.

unbeaten / unbeatable
Loading your saved state.
unbeaten
Not having been defeated in a competition, fight, or game.
Die Mannschaft ist in dieser Saison noch ungeschlagen.
The team is still unbeaten this season.

The word consists of the prefix 'un-' (negation) and 'geschlagen' (beaten), the past participle of 'schlagen' (to hit/beat). So it literally means 'not beaten' or 'undefeated.'
Der Boxer ist in seiner gesamten Karriere ungeschlagen.
The boxer is unbeaten in his entire career.
This meaning is used almost exclusively in the context of sports, games, or other competitions. Look for words like 'Mannschaft' (team), 'Spieler' (player), 'Saison' (season), or 'Turnier' (tournament).
Die Mannschaft blieb die ganze Saison über ungeschlagen.
The team remained unbeaten throughout the entire season.
In the meaning 'unbeatable' or 'unsurpassed,' the word is often specified more precisely by an adverb like 'preislich' (in terms of price) or a prepositional phrase like 'in puncto Qualität' (in terms of quality). It usually comes at the end of the sentence.
In Sachen Benutzerfreundlichkeit ist diese App ungeschlagen.
In terms of user-friendliness, this app is unbeatable.
to put underneath
In this contrast, 'unterlegen' is not meant as a separable verb, so not in the sense of 'to put something under something'. The adjective use is meant here: someone who is 'unterlegen' in a game or competition loses or is weaker. 'ungeschlagen', by contrast, means that someone has not yet been defeated. So the contrast lies in the outcome of a competition: 'unterlegen' means defeated or not strong enough, while 'ungeschlagen' means unbeaten so far.

Nach zehn Spielen ist das Team immer noch ungeschlagen.
After ten games, the team is still unbeaten.
Im Finale war unsere Mannschaft dem Gegner klar unterlegen.
In the final, our team was clearly outmatched by the opponent.