I got a great tip from a collegue (my mentor) for when other people try to take over or try to derail me.

Every time they interject a comment say "That's very interesting, thank you. Now back to my topic" (and then go right back to your next statement/sentence, etc). You end up essentially cutting them off without getting flustered and still sound professional. It makes them shut up (after you have done this a few times) as they are getting no satisfaction/fun out of making you have a melt down.

In other words: when somebody wants to you get into a contest of tug of war, don't pick up your end of the rope