Essential Qualification vs higher qualification

In a certain Govt Job advertisement essential qualification was asked for diploma in engineering. there was a total of 10 post. 2 post was reserved for SC category. But at the time of selection it has been found that the candidate who appointed was not a diploma holder but a degree holder. but in interview diploma holders was also there and qualified the interview. now the question is can a public service commission overlook the essential qualification as it was clearly mention those post was for diploma holders; even the pay scale was for diploma category? please answer should i go for a petition to high court?