When Lex had realized the strength of the attacking creature was equivalent to an immortal, he almost panicked. The keyword here was almost. Just as quickly as he realized how strong it was, he also realized that the attack lacked the somewhat mysterious yet elusive strength that only immortals had. The unknown elusiveness carried by immortals was something Lex had picked up on after countless hours observing brand new immortals who had just survived their first tribulations. Its attack only matched them in terms of pure physical strength.
If that were the case, Lex decided to take it head on! He used Harden on his body, and Impervious hands to prepare his hands. Then he put as many Imperial shields in between the falling limb and himself. Considering all of this happened in a mere moment, the 2 shields he was able to put up was a testament to his sheer skill with defensive techniques.