As soon as the opening bell rang Kerman Lejarraga came out on the front foot, asserted his dominance and sent Flatley to the canvas in the closing seconds after a left jab stunned the 27-year-old.
Flatley continued to endure a barrage of punches from Lejarraga and looked to use his footwork to keep his opponent at a distance. However, the champion was still able to land eye-catching shots in front of a raucous crowd.
With the fight quickly running away from Flatley, he tried to go toe-to-toe with Lejarraga, but he struggled to land any meaningful shots and was knocked down for a second time following a thunderous right hand in round eight.
It only seemed like a matter of time until the fight was stopped and that time came in the opening periods of the ninth when another right hand knocked out Flatley.
Following what was a brutal finish, Lejarraga showed his class as a champion by encouraging a raucous and hostile crowd to show respect to Flatley who showed real courage during a hard-hitting main event.
This knockout finish topped off a memorable night of boxing in the Basque country which included an impressive first round stoppage win for prospect Samuel Carmona and Campbell Hatton's first TKO in the professional ranks.