Photos: Errol Spence Smashes Bundu Out Cold - Mega Gallery

BROOKLYN - Undefeated rising star Errol "The Truth" Spence Jr. (21-0-, 18 KOs) moved one step closer to a world title as he delivered a thunderous sixth-round knockout of tough Italian contender Leonard "The Lion" Bundu (33-2-2, 12 KOs) Sunday afternoon in the main event of Premier Boxing Champions (PBC) on NBC from Ford Amphitheater at Coney Island Boardwalk in Brooklyn. Photos by Ryan Greene.

With the knockout, Spence Jr. becomes the mandatory challenger for undefeated welterweight Kell Brook and showed his willingness to step in the ring with Brook.

"I definitely want my shot at Kell Brook and his title," said Spence Jr. "I want him next. If he vacates or gets stripped then I'll fight for his vacant title. I've paid my dues."

In a prime spot that immediately followed the U.S. Men's basketball team winning Olympic gold in Rio, the Dallas-native started patiently, measuring his opponent with steady jabs. Bundu came ready to fight and tried to make it difficult for Spence Jr. by switching stances and attacking from awkward angles.

"I was a little shakey in the first round and second rounds," said Spence Jr. "He's very awkward and I was trying to feel him out."

Spence Jr. began to pick up his power punching as the rounds went on and started to connect with left uppercuts and hooks. After round four, Bundu returned to his corner with swelling beginning to show up over his right eye.

"Once I was able to catch his rhythm and figure him out, I knew I had him," said Spence Jr. "I knew he was very tough, but he never hurt me. He was switching and jumping in and out and it took me a little bit to adjust to."

The dominance with his power punches began to wear Bundu down as the fight entered the sixth. After seemingly scoring a knockdown, which was ruled a slip by referee Johnny Callas, Spence Jr. quickly pounced on Bundu and trapped him in the corner.

"He certainly lived up to the hype," said Bundu, who was taken to the hospital for evaluation after the fight. "Errol was more precise than Keith Thurman. Errol threw more punches and was fresh in every round."

It didn't take long for Spence Jr. to take advantage as he hit Bundu with a hard left uppercut and followed with a crushing right hook that put Bundu on the mat for good and forced the referee to stop the fight at 2:06 of the sixth-round.

"I really tried to get up but I couldn't," said Bundu, who had never been stopped before. "I am okay though. I feel good."

Spence Jr. won every round on all three judges' cards and landed a staggering 64 percent of his power punches, per Compubox.

"I think this performance showed once again that I am one of the top fighters at 147-pounds," said Spence Jr.