During the fight Williams looked to have been working off his left jab while Tillman was focusing on throwing big punches.
There was a short period where it looked as though Tillman was trying to give Williams a false sense of security to draw him in close enough to attack with his big blows. It didn't last long.
A connecting left punch from Williams rattled Tillman - whose professional record before last night included 21 fights with 11 wins, eight losses and two draws- which was when Williams said his "Samoan nature" kicked in.
At a press conference after the match Williams said that once he realised his hits had done some damage to Tillman, survival-mode kicked in and he took advantage of the situation.
"I was shocked that he got rattled ... my Samoan nature just took over," Williams said.
He said his New Zealand title was just like winning a world title.
"For me it was my world title.
"Nothing compares to that."
The scuffle at the weigh-in the day before - which involved Tillman trying to intimidate Williams by shoving and punching him - gave the local rugby star extra motivation for the fight, he said.
"He got his punch in at the weigh-in, but I got him in the end."
At the end of the one-round fight, the Williams camp couldn't hide their excitement with huge smiles, bouncing inside the ring, big hugs and raising Williams into the air.
Tillman on the other hand left the ring without his crew and walked out of the Arena, surrounded by loud booing by the crowd.
Back inside the ring, Williams' original competitor Richard Tutaki had jumped in to call him out and also unsuccessfully tried taking the microphone from the commentator.
But what's next for Williams' boxing career?
It's undecided at this stage but, in the meantime, Williams will be back training with his Chiefs team mates on Monday.
