I have a master degree and 2 years of experience. An employer has a job position requiring "a bachelor degree plus 5 years of progressive experience", and they may offer me the position and sponsor the Green Card application in EB-2 of PERM labor certification.

But the employer also said that this job only needs a bachelor degree, not a master degree. Since I have a master degree and am qualified for EB-2, I figure that I can apply for EB-2, even the job only needs "a bachelor degree plus 5 years of progressive experience". Am I right?

The USCIS uses the qualification requirements in the PERM labor certification application to determine whether the alien beneficiary is qualified for the job. It is true that both the requirement of a master degree and the requirement of a bachelor degree plus 5 years of progressive experience are separately qualified for the EB-2. But it does not mean that one qualification can substitute the other alternative qualification requirement. 

The PERM labor certification for EB-2 includes master degree requirement, or bachelor degree plus 5 years of progressive experience requirement. In your case, you only have a master degree and 2 years of work experience, you can apply for labor certification with your master degree if the job position requires the master degree. But you cannot apply for the labor certification with a job that only requires a bachelor degree plus 5 years of progressive experience.