Starkiller's talent to be a duelist was so formidable that he could overcome most opponents with small trouble, with only Darth Vader having the ability to stand from him for an important amount of time. The Dark Apprentice was ordered by Darth Vader in the last scene of Distant Thunder https://mixbookmark.com/story5315100/the-smart-trick-of-raffi777-that-nobody-is-discussing