Root made a tonne on day three of the second Test as the visitors closed with a lead of 278 runs.
England at stumps were 324 for 9, following the Lankans first innings total of 336.
Root's knock is record breaking as its the highest by an England skipper in Sri Lanka.
"You have to enjoy good days because there are plenty when it doesn't go your way," Root told the BBC.
"It is hard to compare [centuries] but it definitely feels like it is the best at the moment.
"On a surface like that, where at times you can feel very vulnerable, it was very enjoyable."
England lead the Sri Lankans 1-0 after scoring a victory in the first Test in Galle.