I can't promise you will win, but I can tell you how to defend yourself.
1. Do not admit to slowing only 10 mph below the speed limit. If you do, then you're guilty, no matter what other mitigating circumstances there may have been at the time.
2. The officer could not possibly have been able to obtain an accurate measurement of your speed, because this was an emergency situation -- so, the officer was almost certainly guessing at your speed. This puts you in a better position to state your speed, than the officer, and you may want to bring this to the court's attention (unless, of course, the officer tesifies that he/she was using radar/lidar, in which case, the question becomes: "Considering the emergency nature of the circumstances, how is it that you chose to set up to use a speed measurement device, rather than to help with the emergency?" In other words, you want to make the officer look ridiculous, so that your closing argument can be, "Your honor, under the circumstances, there is simply no way that the officer could have measured my speed, and if he/she was, then he/she was derelict in performing his/her duties as an officer in an emergency. The officer is clearly inventing a story, and his/her testimony should be given little if any evidentiary weight. The defendant was in a far better position to know his/her speed at the time of the alleged violation, and should be found not guilty."
That's how I'd do it.
Hope this helps.