The 24-year-old was the key to Malaysia's second half revival to hand Keisuke Honda a 1-3 debut defeat as the new manager of the Cambodian national team.
Shahrel came off the bench in the second period as Tan Cheng Hoe reverted to a more conventional 4-4-2 that sparked the comeback for the Malayan Tigers.
Early warning signs were already there with a couple of free kicks when Thierry Chanta Bin crashed one effort against the bar and then Khairul Fahmi had to drop low to stop another attempt.
But Malaysia failed to heed the signs and Cambodia took the lead from a free kick routine in the 18th minute.
Chanta Bin's cross floated to the far post and Keo Sokpheng's header was thrashed in by Souey Visal via the head of fellow centre back Hong Pheng.
Malaysia looked in complete disarray and struggled to even string a couple of passes together. Cambodia pressed high and in numbers, which forced wayward passing off the away team.
Tan was forced to an early change when Nasir Basharudin had to come off due to injury with Azzizan Nordin given his first taste of international football.
But it was the change of Shahrel for Nazmi Faiz that turned the game in favour of Malaysia. The Nakhon Ratchasima forward directed a header in the 57th minute that gave Shahrul Saad the chance to stab home the rebound.
Just 17 minutes later, Shahrel shrugged off the tug from a Cambodian defender to drive towards goals before delivering the perfect cross for Syazwan Andik to head in the winner.
But that wasn't to be the end of Shahrel's contribution as the forward also lashed home a third for Malaysia in added time to earn himself a first senior goal for the country.
The win extended Malaysia's eight games winning run over Cambodia that dated back to 1971 to nine games.
As the Malaysian players head back to club duties, they will no doubt returned in a positive manner having helped Tan secure his third win in four matches.