Sam almost waited for 3 hours and finally, he could see that one Monster going separate ways from those other Monsters. Naturally wasting no time he began to follow that Monster and sometime later both of them came to a place where most likely The Monster wanted to see if any other new Monster entered their area or not.
The Monster most likely scouting the area that was under them. Naturally, The Monster did not notice that Sam was very close to him and he was already ready to use his techniques to kill that Monster without giving him the time to react or do anything.
Sam from the first decided to use 100% of his power to kill that Monster as quickly as he could as he did not want to attract those other Monsters which could be dangerous for him.