Unified middleweight titlist Gennady Golovkin and secondary titleholder Daniel Jacobs on Monday were formally ordered to meet in a mandatory bout, the WBA announced.
"The 30-day negotiations period has started," WBA president Gilberto Mendoza Jr. said. "They have 120 days to do the fight."
If the camps do not come to an agreement before the deadline, a purse bid will be ordered.
Golovkin and Jacobs are both coming off knockout wins in recent days and are on the same schedule, with Golovkin tentatively slated to return Nov. 26, the date HBO is holding for him.
On Friday night, at Santander Arena in Reading, Pennsylvania, Jacobs retained his version of the title for the fourth time by knocking out former junior middleweight titlist Sergio Mora in the seventh round of their rematch. Jacobs, who stopped Mora in the second round 13 months ago, dropped him five times in a one-sided fight.
On Saturday night, at the sold-out O2 Arena in London, Golovkin stormed to a knockout of welterweight titleholder Kell Brook, of England, who moved up two weight divisions for the fight. Dominic Ingle, Brook's trainer, threw in the towel during the fifth round as Golovkin battered Brook along the ropes. Brook suffered a broken orbital bone around his right eye.
Golovkin, who holds three major world title belts, retained his title for the 17th time, as he scored his 23rd knockout in a row.
A fight between Golovkin and Jacobs, also a big puncher, would give them both the opportunity to fight a top opponent in the division; both said they are interested in the bout.
Days before the fight with Mora, Jacobs said: "We want to fight the best, point blank, period. GGG is the best, and that's the guy that we want."
He called out for Golovkin again after knocking out Mora, saying: "I want to prove to the world that I'm the best middleweight. If GGG gets the victory [Saturday], that's who we want."
Golovkin (36-0, 33 KOs), 34, a Kazakhstan native living in Santa Monica, California, has campaigned for the fight most fans want to see, a showdown against lineal champion Canelo Alvarez, but Alvarez has avoided him. Golovkin also would like to fight Billy Joe Saunders in a unification fight so he can have a chance to claim the one major belt he does not already own. But Saunders has also dodged him, so Golovkin said he would love to face Jacobs, 29, of Brooklyn, New York, who is one of the top middleweights in the world.
"Daniel Jacobs, he is very good fighter. Huge fight, probably in New York," Golovkin told ESPN.com in his dressing room after stopping Brook. "Absolutely. I am open for everybody. I think right now this is best fight for us."
It will come down to whether the sides can make a deal. Golovkin is under contract to HBO, and Jacobs (32-1, 29 KOs), while not signed to a television network, is managed by Al Haymon and part of the Premier Boxing Champions series. Haymon's fighters, at one point banned by HBO, have been allowed to appear recently as B-sides to star fighters.
Dominic Wade, a mandatory challenger, got knocked out by Golovkin in April on HBO, and Amir Khan got brutally stopped by Alvarez in May on HBO PPV.
Whether Haymon will negotiate for Jacobs to face Golovkin remains to be seen. If it goes to a purse bid it would be fascinating to see if Haymon will use his diminishing PBC war chest to try to outbid Golovkin's camp, which has support from HBO. But the network's budget appears to have taken a big hit this year.