Hong Kong-based contender Rex Tso came out on top of a wild brawl with Japan’s Hirofumi Mukai, scoring an eighth-round knockout in front of a reported 8,000 fans in their junior bantamweight fight at Hong Kong Convention and Exhibition Center on Saturday night.

Tso (21-0, 13 knockouts) scored knockdowns in rounds three and six before finishing Mukai (13-5-3, 3 KOs) at the 32 second mark of the eighth. A straight left to the body by Tso put Mukai down for a third time, convincing referee Danrex Tapdasan to waive off the bout.

Despite the knockdowns, the fight was touch-and-go for much of the affair, with both men starting out with jabs before opting to trade power shots midway through the first round. Mukai found himself bleeding from his left eye due to an accidental headbutt by the time the round ended.

Mukai, who had twice challenged for world titles, settling for a technical draw against Pongsaklek Wonjongkam for the WBC flyweight title in 2011, and being stopped in nine by Srisaket Sor Rungvisai for the WBC junior bantamweight title in 2013, got the better of the action in round two by counter punching off Tso’s aggression. Tso later told the crowd he had lost hearing temporarily from a left hand in that round, according to the South China Morning Post.

Mukai found himself on the canvas early in the third off a quick straight left. Once he rose up, Mukai fought even harder. Tso landed shots as he attempted to finish him but Mukai had his opportunities as well, firing back with fewer punches but landing with eye-catching, flush shots.

But the pressure Tso put on Mukai – and his subtle advantage in technique – and Mukai appeared weary as the fifth round ended. A right hook in exchange put Mukai down in the sixth round, and he was saved by the bell once again in the seventh. The end was preceded by a barrage of a dozen punches along the ropes for which Mukai was unable to answer.

Tso, 29, is rated in the top 15 by all four of the major sanctioning bodies (No. 1 in the WBO, No. 7 in the IBF, No. 10 in the WBA, and No. 12 in the WBC) at 115 pounds. Tso’s manager Jay Lau tells RingTV that the plan is to have him face former WBA junior bantamweight titleholder Kohei Kono (32-10-1, 13 KOs) in October. Lau says he will be traveling to Tokyo on Tuesday to discuss the fight with Kono’s manager Hitoshi Watanabe.

The 36-year-old Kono is coming off back-to-back losses to Luis Concepcion and Naoya Inoue.

In earlier fights, Mark Anthony Geraldo (34-7-3, 15 KOs) of Kibawe, Bikidnon, Philippines scored a 10-round unanimous decision over Kenny Demecillo (12-4-2, 7 KOs) of Iligan City, Lanao del Norte, Philippines to win the vacant WBO Oriental bantamweight title

Geraldo and WBO bantamweight titleholder Marlon Tapales had been Tso’s chief sparring partners to prepare for this fight.

Filipino journeyman Rey Megrino (24-20-4, 21 KOs) needed just 23 seconds to finish Japan’s Yuki Strong Kobayashi (10-7, 5 KOs), knocking him cold with a single right hand.