If you are the first to make the move, and they don't instantly change the course of their entire formation to follow, you build up a LOT of range and momentum that is separating the two forces. They have to not only match your course, which will take time and fuel, but also EXCEED your acceleration in order to first match your speed and then start gaining on you. In short, if you pick your moment and choose a course diametrically opposed to their course, you are GONE unless they have a CLEAR advantage in either fuel (long term) or acceleration (short term) over you.
This all assumes that you started the battle at zero relative velocity. Either side can choose to perform a high speed engagement run though, limiting the engagement to two or three minutes of firing.
In short, with proper planning and good instincts, it is easy to use momentum and thrust to limit the time of any battle down to the point that you can get most of your ships out of even a losing battle. Not all by any means. You WILL lose ships. And if they are willing to spend their time hitting your big guns, you will lose a lot of THOSE while your smaller ships survive. But it is easy to force them to let MOST of your ships get out, UNLESS the majority of their fleet has either a fuel (long term chase) or acceleration (short term chase) advantage on you.
Period. End of Line.