first battle; first campaign; debut fight
Originally a military term for a warrior's first battle; now also used figuratively for one's first attempt at any challenging endeavor, such as a competition, exam, or new job.
彼は初陣で見事な勝利を収めた。
He achieved a splendid victory in his first battle.
The rookie player's debut match is next week.
The rookie player finally made his debut.
He won brilliantly in his first battle.
She is about to face her first battle next week.