With senior Isaiah Lewis out with an injury, Williamson was in the starting lineup for the first time.
"RJ might as well be a starter," defensive coordinator Pat Narduzzi said. "That's why we told Isaiah to take it easy. RJ is a great player and we have a lot of confidence in him and you can pretty much say he's a co-starter back there.
"It was great to see him come in and play well."
Williamson said it felt great to get his first start, but he approached it like any other game.
"I prepared for it as I normally would do," he said. "Our coaches always tell us, if somebody goes down, there's always the next guy up. They're never nervous about anything like that. We just gotta go out there and prove it."
Williamson had six tackles and a pass breakup in Spartans' 55-17 win.
"I felt I had a decent all-around game," he said. "There are something I could have done better. I made some nice tackles, but my mindset is just to go out there and do whatever is needed for my team to succeed."
He said the secondary – and the defense as a whole – has the mindset that when the backup steps in that there isn't a dropoff.
"Our defense is full of guys and full of talent," Williamson said. "It's only a matter of time before you se those guys showcase their talents as well. After this year, when some of those seniors are gone it will be the same thing I promise you that."