According to newly corned unified champion Jeison Rosario, he knew right away that Julian Williams was being affected by his power.

On Saturday night, 2020 received what may become the 'Upset of The Year' - as Rosario captured the WBA, IBO and IBF junior middleweight titles with a shocking fifth round stoppage of hometown favorite Julian "J-Rock" Williams at Temple University's Liacouras Center in Philadelphia.

Some betting circles had Rosario listed as high as a 30-1 underdog.

"As soon as I stepped into the ring, I knew he could not hurt me," said Rosario. "I knew that my power was affecting him right away. This is a big victory for me and for the whole Dominican Republic."

In his first world title fight, the Dominican Republic's Rosario landed power punches from the outset and opened up a cut on with a punch over Williams' right eye in the second round. Williams was landing power punches of his own, but was unable to stop Rosario from coming forward.

"I'm so emotional in this moment right now," said Rosario. "When I lost my last fight I said I will never lose again until I become champion of the world and that's what happened tonight. I came prepared. I knew before the fight that I was going to win it."

In round five Rosario landed the punches that would ultimately lead to the end of the fight, hitting him with hard straight right hands that immediately slowed Williams.

"I have to give a lot of credit to my team," said Rosario. "I had a 16-week training camp and that prepared me for this. My life is changed forever and I can support my family in a whole new way. I realized that I was going to win, once I was offered the fight. I knew that if I made the sacrifice, that I would do what I did tonight. I knew it 16 weeks ago."

Rosario sensed his moment and came forward with big punches, while Williams tried to hold and survive. Eventually the onslaught proved to be too much, and referee Benjy Esteves halted the bout 1:37 into the round. At the time of the stoppage, Rosario led 39-37 on two cards, with the third card scored 38-38.