# n+l rule for first member of lanthanide and actinide series

as we all know that if the value of $$n+l$$ is same then the orbital with lower value of $$n$$ will get filled first so in case of first member of lanthanide series the configuration is $$(\ce{Xe})\mathrm{6s^2 5d^1 4f^1}$$. Here, the $$n+l$$ value for $$\mathrm{d}$$ orbital and $$\mathrm{f}$$ orbital is same i.e. 7 and $$\mathrm{4f}$$ have a lower value of $$n$$. Then why are we not filling the electron in $$\mathrm{4f}$$ first?