Ceire Smith stopped Krisztina Beri to get Ireland's European Women's Elite Championships campaign off to a winning start in Madrid.
The Cavan flyweight forced the Hungarian flyweight into taking three counts in the second round as the referee waved to contest off.
Smith will face Turkey's number one seed Naz Buse Cakiroglu in the last 16 on Monday.
Roscommon middleweight Aoife O'Rourke meets Ukraine's Tetiana Petrovich with at least bronze up for grabs in the quarter-finals on Monday, while Dundalk lightweight Amy Broadhurst is in action against Dominika Ciklova of the Czech Republic in the last 16.
Cork Christina Desmond goes head-to-head with Dutch welter Anna Van Leeuwen in the last 16 on Tuesday.
Head coach Zaur Antia and Damian Kennedy are working Ireland's corner in Madrid.