She was wary of Kiesanowski, the 2003 national champion and three-time Olympian.
"She's had a phenomenal career and she's won some big sprints internationally and I know Georgia, we train on the track together, so I know what's she's been doing for training and that she'd have a good kick as well.
"I knew I had to lead it out and I just feel the moment and put my head down."
The trio formed at the front of the race after the third time up the Spencer Road climb, when Williams led the chase group up to breakaway riders Ruby Livingstone and Sharlotte Lucas.
"I was feeling quite strong on the hills so I figured that's the only way it will split it up," Williams said.
It's the second time the 22-year-old has had to settle for second in the road race, but she is satisfied after missing out on the podium in the time trial.
"I know Rushlee and Jo are both such good sprinters, so I was a bit worried," Williams said. "I'm happy with second. It's fine."
Buchanan will now turn her attentions to the track in the lead-up to the Rio Olympics, but will take her national champions jerseys to the US where she rides for United Healthcare.
"It's such an honour to wear one so to be able to wear three, I don't really have any words for it and I probably won't feel the enormity of it until I wear the silver fern this year."