Our team last year's winners 5-0 in the first round of the tournament.

defeated

Explanation:

The sentence is talking about competition between two teams hence only two words can suitably answer the question, victory and defeat.

Since the sentence says about last year winner and speaker tries to express some accomplishment by laying emphasis on winner adjective for opponent. It clearly suggest that they got better of a competitive team.

Hence defeated is the most suitable answer to this question.