So I kept pushing myself. Next thing I know, I'm rounding the corner and I see the finish line just a block away. And now for the SUPER obnoxious part. Two or three serious-runner-looking types who were off in the grass watching the race suddenly join the girl who had been walking/sprinting ahead of me to encourage her to kick it in high gear to finish. Well, apparently she crashed and burned because I'm the one who found my second wind and sprinted to the end, kicking her butt - it felt AMAZING!!
The next race on the circuit: a 10-miler at the end on October, twice as long as any race I've ever attempted. Looks like I've got some work to do.