I've started introducing walk breaks at specified intervals. Today I did 5 minutes running/1 minute walking (though I shortened the last walk break to about 15 seconds.) I was able to push my speed during the runs. It was challenging, but WOW! Previous best 5K pace was 10:02/mile; today was 9:24/mile! Walk breaks work! It also helped that I did a half mile warm-up before starting the clock for the 5K.
3.1 miles, 29:09 (9:24/mile)
Warm-up: .48 miles, 6:08 (12:46/mile)