Legs running fast than lungs

I wanted to break my 5km record (23.26) this morning but just under half way through I was not able to keep up the required pace to get under 23.26 and finished in 24.06. I am pleased with the time but I would love to get even faster and push up more levels. Something I noticed was that my legs were able to maintain the required pace and didn't hurt but it was the breathing which was harder. I am a non smoker and just want to know how I can get my breathing at the same level as my legs so that I can push past my record.