For Prendergast, it was a mixed opening half-hour as he was given a chance to showcase his abilities from the start for the first time.
There has been a lot of hype and expectation after the emergence of of the 21-year-old as he looks set to challenge Jack Crowley, who is currently Ireland's first-choice, and Ciaran Frawley, for the starting jersey at fly-half.
It was a rocky start. Minutes after landing his first conversion, Prendergast was shown a yellow card after a clumsy shoulder hit on Kitone Salawa.
He then sent a kick out on the full and squandered a try-scoring chance after hesitating on playing a killer pass, but settled and his standout moment came when his inch-perfect kick into the corner landed in the arms of Mack Hansen, who scored on the stroke of half-time.
Prendergast continued to conduct the backline, which became more makeshift as the game progressed, as he played the full 80 minutes and he kicked five of his seven conversion attempts.
"I thought he did great and he was really composed," added Farrell.
"There were a few mistakes within his game, obviously, but he was pulling the strings for a good while.
"It was tough against Fiji because you don't know what you are going to get at times. I thought it was a great showing from him."
Along with McCarthy, Ulster back row Cormac Izuchukwu was handed a debut from the start in Dublin.
Despite not stealing the headlines, Farrell was impressed with the 24-year-old and called him a "presence".
Izuchukwu quietly went about his business and was unfortunate to have a debut try scrubbed off in the first half after Hansen's pass was deemed to have crept forward by referee Hollie Davidson.
"I was gutted for Izzy with the forward pass," added the Ireland head coach.
"It would have been nice for him to get over the line. I thought he was a presence, certainly in the line out. He's some athlete."