Golovkin floored Monroe twice in the second round and again in the sixth to secure his 30th win inside the distance in his 14th title defence.
The former Kazakh Olympian has now stopped each of his 20 opponents since June 2008, and even a surprisingly strong fourth round from Monroe couldn’t throw Golovkin off his path to the top.
After a solid first round, Golovkin backed Monroe against the ropes in the second and knocked him flat with a textbook-perfect left hook to the head. The challenger wobbled while getting up slowly, and Golovkin put him back down moments later with a big right hand.
Monroe made it to the bell and even recovered to land several big shots in the fourth round, but Golovkin buckled his knees again in the fifth before finishing the sixth in style, pursuing the ducking southpaw around the ring until finally landing the knockdown punches in the sixth.
“It was a good big drama show,” Golovkin said. “I was happy with my performance. Willie is a very tough fighter. I felt very strong tonight. I knocked him down twice, but I didn’t want an easy round the next round. I wanted to keep working.”
When Golovkin floored Monroe (19-2) with a long series of heavy punches in the sixth, the challenger declined to continue after his final trip to the canvas.
“I’m done,” Monroe told referee Jack Reiss.
Golovkin, who intends to fight two more times this year, called out Miguel Cotto and Saul ???Canelo??? Alvarez after the victory.
On the undercard, Nicaragua’s Roman “Chocolatito” Gonzalez also defended his WBC flyweight title in style at Inglewood???s historic Forum in California with a furious second-round stoppage of Mexican veteran Edgar Sosa.
Gonzalez (43-0, 37 KOs) battered Sosa, a talented veteran contender, around the ring in the first round and dropped him three times in the second.
“I’m very happy with my performance,” Gonzalez said. “He was a tough fighter, but my power was too much.”
Throwing sharp combinations and showcasing power in both hands, Gonzalez floored Sosa (51-9) twice with brutal right hands before finishing him with a multi-punch barrage against the ropes with 23 seconds left in the second round.