Slight setback?

Went out for my planned 20 miler Sunday at 9:45am with rain coming down and a large cloud hanging over the Greenville radar, but scattered showers behind it - so some respite from the wetness, supposedly. 40° temps weren't horrible either but I had to throw on one more layer under my windbreaker before I started and it worked out just fine. The rain went on and off form "steady" to "heavy" and back and forth repeatedly. I just had to laugh out loud at one point it was so ridiculous out there, doing laps, watching the sides of the road get filled with water. My heron showed up for a lap, so I take that as a good omen - even though I had to walk much of the last 2 laps. My on and off left ankle/shin was sore the night before for no reason, then crept up on me after 5 miles or so. I was really worried I'd have to stop after a 10k or so, but it never got too bad. It eventually went away after 15 miles or so, then I proceeded to have my 3 fastest laps (trying to go for even splits and making up for my 3 Gu breaks). My last little break did me in though - More pain that had me slowly walking, trying to shuffle the remaining two miles. I wanted that 20 (actually - 20.4 miles). My 9:02 pace thru 18 miles turned into a 9:17 overall, but that's ok. Finishing is my goal as always, uninjured is up there too. Third goal is the even split times. One thing different about this run - even during nd after those faster laps towards the end - no heaviness or soreness in my thighs or hips - and that is always where I feel it, the speed tapers off and I have to mentally push myself to continue.
More to follow on this. Extra rest day tomorrow.