0750 GMT April 08, 2020
The 33-year-old floored Monroe twice in the second round in Inglewood, California before landing the decisive blow 45 seconds into the sixth, BBC wrote.
The former Kazakh Olympian, defending his title for a 14th time, has knocked out all his opponents since June 2008.
He said, “It was a good, big drama show. I felt very strong.”
Facing an awkward southpaw counter-puncher, Golovkin who has stopped 30 of his 33 opponents inside the distance, delighted a crowd of 12,372 in his adopted home with a display of powerful shots.
Monroe, who lost for the second time in 21 fights, showed his resilience by climbing off the canvas twice in the second round but Golovkin landed a long series of heavy punches in the sixth until the challenger declined to continue.
“I’m done,” Monroe told referee Jack Reiss.
Golovkin is keen to capitalize on his growing reputation as one of the world’s pound-for-pound best fighters and after the fight he called on Miguel Cotto and Saul ‘Canelo’ Alvarez to face him in the ring.