Golovkin (30-0, 27 KOs) floored the 33-year-old Geale (30-3, 16 KOs) in the second and then continued to mercilessly stalk the bleeding Aussie.
Sensing a beaten man, Golovkin exchanged punches with Geale in the third and landed a savage right hand that again sent the former two-time middleweight champion to the canvas.
Although Geale managed to regain his footing, referee Michael Ortega compassionately halted the bout at 2 minutes and 43 seconds of the decisive frame.
A bruising, ferocious and accurate slugger, Golovkin has never been toppled in over 375 contests.
"I was patient in the first round and part of the second round, but once I figured him out I was able to attack aggressively. I knew it was a matter of time,” said Golovkin, 32, who captured a silver medal at the 2004 Olympics in Athens and now owns a 90 percent knockout ratio as a professional.
"I am very happy and now I only want unification fights. I want [Miguel] Cotto. I want to fight Miguel Cotto and I want to fight him next. I want prove to the world that without a doubt that I am the best middleweight in the world. That is very important to me."
Meanwhile, in a similarly dominating manner, the 33-year-old Cotto (39-4, 32 KOs) pulverized Argentinean Sergio Martinez to earn the WBC middleweight crown in June.
Meeting at a maximum weight of 159 pounds, the 5-foot-7 Cotto grounded the 5-foot-10 Martinez (51-3-2, 28 KOs) three times in the first and once more in the ninth and was ahead 90-77 on all three scorecards when trainer Pablo Sarmiento wisely ceased the beating.
Looking reenergized and throwing fists with a noticeable confidence, Cotto became the first Puerto Rican boxer to win world titles in four weight classes.
Cotto is tentatively slated to reenter the squared circle in December versus an opponent to be named.
If the courageous Puerto Rican chooses to scrap the “Good Boy,” the 5-foot-11 Golovkin will punish Cotto and record his 18th consecutive stoppage.
Ultimately, against Miguel Cotto, Gennady Golovkin would verify that he is “the best middleweight in the world.”