Of course Zoro wasn't going to win but he is not fighting Imu either, its just an initial clash and Zoro is now going to do something else it seems.
I think the difference is clear that Oda didnt have Imu use a named attack against Sanji and Hajrudin and just big explosions. Another detail that someone pointed out on twitter is that Zoro actually reacted to the point blank attack, notice his swords at the time of attack and at the time of Imus attack. Maybe thats the reason there wasn't an explosion and Zoro is still conscious. He couldn't block the whole attack but still managed to react to that point blank attack.