Notes
Went out to follow the 22 pacer but they got held up in the crowd at the start so went with the 21 one. The first km was fast so he (I assume) backed off but I didn't. I knew at 3km that sub20 was off the table (even though the markers were earlier than the watch) so slowed down a bit.
Finished comfortably ahead of the pacer so was surprised to have come in at 21 dead to the millisecond.