Shaiful is widely regarded as first choice left-back for the Lions, his delightful left foot capable of testing opposing goalkeepers or providing sumptuous crosses in equal measure.
However, Irwan is believed by many to be the heir to Shaiful's throne, and - at the tender age of 23 - he has already established himself as the player most likely, in time, to usurp Shaiful and make the left-back position his own.
Ahead of next week's World Cup qualifier against Iraq, Irwan took time out to pay tribute to his senior colleague, while making it clear that he intends to continue staking a claim for a starting berth.
"Everybody in Singapore football knows that nobody can strike a ball better than Shaiful down the left flank," he told Singapore's national team media officer Kelvin Leong at the team's training camp in Dubai.
"Being in the same team as him gives me an opportunity to learn his wonderful technique, but that does not mean I will give up my chance of dislodging him as the starting left-back for the national team.
"He (Shaiful) is my biggest enemy but also my main motivation," Irwan, who has featured for the National Football Academy, the Singapore Armed Forces Prime League team and the Courts Young Lions, added.
Irwan's tenacious style of play has always been one of his strong points. That, coupled with his admirable never-say-die attitude, makes him an ideal addition to any team - be that with Singapore in the international arena or for LIONSXII in the Malaysia Super League.
"When I started playing football with my father's friends and through my primary and secondary school days, I always felt a need to be aggressive in order to compensate for my physique,' declared the talented left-footer.
"I always believe in giving my all, and I try to make it as tough as possible for opponents to help my team win matches."
Seen as a tough warrior not only on the pitch but off it also, Irwan - rather refreshingly in this era of inflated footballing egos - remains grounded enough to admit that he attributes his success to two women, both of whom have had a profound influence on his young life.
"My mother, Madam Kamsihatun has never missed a single match that I have played in Singapore," he proclaimed.
"Since my primary school days, she faithfully attends every match to support me. I remember there was once during my Centre of Excellence days, I was embarrassed as a teenager that my mother wanted to come watch me play and I told her not to show up! Looking back, I definitely regret telling her that but I am glad she showed up despite my silly request."
The other significant woman in his life is Irwan's 22-year-old fiancé, Farhanah. The couple will be getting married in 2013.
"I met her (Farhanah) at a game of futsal and it took me two years before she agreed to be my girlfriend," Irwan explained.
"Then, after two years of dating, I decided to discuss marriage with her. She agreed on the spot, but it was only a week later that it was confirmed as I had to ask her parents for her hand. She is an important person in my life and has always been supportive of football as my career."
With two wonderful women in his life to offer constant support, as well as a bucketful of talent, it seems as though it will only be a matter of time before Irwan gives his mentor, Shaiful Esah, a real run for his money.
Singapore take on Azerbaijan in a friendly on Thursday, before playing Iraq five days later.
Image courtesy of the Football Association of Singapore