Just 21, he has earned his first start after showing admirable composure last Friday when he came on for Jack Crowley on the hour mark with Ireland struggling to keep their noses in front of Argentina.
The Irish did not add to their points tally of 22, but they held on to win 22-19 and Prendergast's performance had head coach Andy Farrell purring.
"I thought he was excellent," said Farrell.
"I thought he was really composed, playing your first cap in that type of position, that type of situation.
"He played at a nice tempo at the line and started to make things happen. That just shows what type of character he's got."
It is too early to say whether he is the answer to filling the huge vacuum left by the legendary Johnny Sexton, who retired after last year's Rugby World Cup quarter-final defeat by New Zealand.
The Fijians, though, will provide a stern test both physically and in terms of attacking flair -- the latter quality something Prendergast would admire as it has been his trademark at Leinster and the successful Irish Under-20 side.
Sometimes his desire to produce the unexpected has rebounded and it was a reason Farrell sent him on the recent Emerging Ireland tour of South Africa.
However, he was the only player to start all three matches and impressed Farrell.
"In his own mind he'd probably thought he's been ready for quite some time because he's that kind of kid, a confident kid," said Farrell prior to the Pumas Test.
"The reason for taking him on the Emerging tour was to make sure that he understood what it was to grab hold of his team and show that he is in charge.
"He showed that in abundance.
"In his own mind he's ready.
"He's going to make his mistakes, but that's the nature of anyone coming through."'Too small'
Comparisons with Sexton will be inevitable, and they were already coming after his cameo performance against Argentina.
Former Ireland and Lions back Shane Horgan said his decision-making had reminded him of his former Leinster teammate.
"I love that, it's Sexton-esque, he caught the ball underneath his left shoulder and is ready to pull the trigger at exactly the right moment and he chose the right moment more often than not," Horgan told Virgin Media TV.
Former Ireland fly-half Tony Ward also saw something of Sexton in Prendergast.
"Sexton's greatest asset as a threat to the opposition was his willingness to take the ball where others feared to tread and then by way of timing and quality of pass open gaps close in and wider out," he wrote in Irish newspaper The Sunday Independent.
"It's very early days yet but certainly signs are of a similar tactical mindset in Prendergast."
However, others worry about his relatively light physique and believe that Crowley, who has been first choice since Sexton stepped down, is better suited to the rigours of Test rugby.
"At the minute, he (Prendergast) is too small," former Scotland international Jim Hamilton told podcast The Rugby Pod this week.
"He's playing against Argentina and he looked physically out of his depth.
"Attack-wise, looked great.
"I'm not liking the criticism Jack Crowley is getting.
"He made a couple of errors in the game, but first half I thought he was brilliant.
"Sam Prendergast will come through at some point.
"Everyone is talking about him but he ain't ready."
