Photos: Gennady Golovkin Edges Daniel Jacobs - MEGA Gallery

Gennady Golovkin earned a unanimous decision over Daniel Jacobs on Saturday to retain his middleweight titles, but boxing's knockout king failed to extend his 23-fight KO streak. Photos by Ed Mulholland/HBO.

Golovkin was forced to go 12 rounds for the first time as a professional as Jacobs gave him all he could handle in front of a boisterous crowd at Madison Square Garden.

Golovkin retained his WBC, WBA, IBO and IBF belts as two of boxing's pre-eminent punchers put on an entertaining show against the best opponents of their respective careers.

Cancer survivor Jacobs was an underdog going into the fight but he used his 10-pound weight and reach to his advantage and possibly provided the blueprint for Canelo Alvarez to use against the 35-year-old Kazakh in a future title fight.

Golovkin, who improved to 37-0, won on all the judges' scorecards but the fight was close throughout. He floored Jacobs early in the fourth round with two successive overhand rights to record the only knockdown of the fight.

Golovkin had won 33 of his previous 36 fights by knockout as his 23 fight knockout streak, which dated back to 2008, came to a halt. He has a 92 percent knockout rate, the best ratio of any middleweight in boxing history.

Golovkin's IBF title was not on the line because Jacobs declined to attend the Saturday morning weigh in. Jacobs needed to be within 10 pounds of Friday's official weigh-in weight or lose the chance to fight for the IBF title.

The 30-year-old Jacobs decided the extra weight in the ring was more important than fighting for all of Golovkin's titles and the gamble almost paid off. He dropped to 32-2, with 29 knockouts.

Jacobs is nicknamed "Miracle Man" after his career was almost ended in 2011 because of osteosarcoma, a rare form of bone cancer. He made a full recovery but spent 19 months out of the sport while battling and recovering from cancer.