As an ardent follower of the late Harry Potter, Alexi obviously knew what the expelliarmus spell looked like. What he didn't know was what the first spell did, so in the short time that he had, knowing he could only block one spell, he allowed himself to be hit by the first, and with his own expelliarmus, blocked the second. There was no force of impact felt by Alexi when he first got hit by the spell, but he quickly started to feel pain gradually increasing in his eyes, as well as tears welling up as a result of the painful stimulus. Quickly, he wiped away the tears and knew exactly what to do.
Alexi, having a large space around him, flew backwards at a great speed, while moving his wand to cast incarcerous, and at a safe distance, he pointed his wand at his own eyes. He made quick movements, and said, "Finite Incantatem." It was the only charm that Alexi had to religiously practice during his healer training, because it was one of the most powerful of all counterspells. Allowing himself to hit the ground softly, Alexi took the moment to wipe the tears from his cheeks with his sleeves.