Alex Johnston has scored an impressive five tries in just three appearances for the Rabbitohs since making his NRL debut in Round 8.

It would have to take an enormous talent to be able to push one of Redfern's favourite sons out of the NRL side, but dynamic 19-year-old South Sydney rookie Alex Johnston has done exactly that over the last month.

With Johnston sending veteran Nathan Merritt and his unprecedented club record of 145 tries back to the North Sydney Bears, the La Perouse junior has kicked off his own first grade career in impressive style, crossing for five tries in just three appearances.

To his credit, Merritt, who returns to the side this weekend, was more than happy to help out his new protégé before his debut game at the daunting Suncorp Stadium in Round 8.

"Merritt is a legend and to replace him, I just wanted to take my opportunity and I'm glad to see him back in the team this week and playing fullback. I have full confidence he'll do a great job," Johnston said.

"He wished me luck and gave me a few tips, to see that he had confidence in me and was happy for me, it really made it easier.

"I am loving every minute of it. I've just come into the side to try and do my role and try and cement my spot and the tries are I guess good in a way to show that I'm doing my best for the team."

While Merritt has been earmarked to fill in the hole Greg Inglis has left at fullback, Johnston was unlucky not to have been picked in his preferred position.

"I've played at fullback most of the time coming through the juniors but I have played wing now and then. It's not really my preferred position but no matter what position I play I try and do my job," Johnston said.

"I'm just happy to be on the field and playing my part."

While Johnston grew up as a Dragons fan, he played a younger version of Inglis in a 2009 promotional ad for the NRL, the same man he has lined up alongside three times in the top grade.

"Don't hold this against me but I liked Mark Gasnier and Matt Cooper [when I was younger]. But obviously when I started playing fullback I watched guys like Billy Slater and Greg Inglis, so they would be my idols," Johnston said.

"To be in the locker room with [Inglis] now and play on the same field, it's a bit surreal.

"He's a great bloke. He's made me feel welcome and he's always helping me out as a fullback and off the field he loves to grab a coffee and just have a chat."

Although he was a Dragons fan, Johnston came through the South Sydney system after pulling on his first footy jersey at age nine.

A decade down the track the livewire newcomer is very happy to be living out his dream with the Bunnies – pushing his University studies aside for the time-being after achieving an outstanding ATAR of 91.8.

"Pretty much when I was told [I was going to debut] I was nervous straight away," Johnston said. 

"Playing first-grade is all I wanted and to hear that news I was nervous and then just excited throughout the week.

"The crowd was crazy. Before the game I was really nervous but once I stepped out onto the field I was excited."

While the crowd at Remondis Stadium on Monday night won't be as jovial as a packed Suncorp Stadium, Johnston will be ready to excite and surprise Rabbitohs fans as he looks to continue his marvellous streak of tries – just like Nathan Merritt was doing at the same age.