If that injured guy had torn space himself, he definitely wouldn't have escaped. Because he was wounded—if he then burned all his power to tear space, Su Yang would absolutely have been able to cut him down on the spot.
So he burned his origin and tricked his own brother, having his brother tear open space, while he himself slipped away through that spatial rift.
Not only that, he even ambushed his own brother, forcing his brother to block Su Yang. That way, his own chances of escape got even bigger.
By the time that second person understood what was going on, it was already too late.
Grievously wounded and facing Su Yang alone, he naturally didn't have the slightest ability to fight back. Before long, he was cut down by Su Yang and then devoured by Su Yang again.
As for that Saint Emperor who fled, Su Yang gave chase for a bit symbolically, but didn't go too far. Because he was deliberately letting this man go.
