I trust that you did a great job in drying the phone. I would make sure that the phone is completely dry inside. If the power button did not experience a physical damage, its malfunction could be related to water inside. And besides that, corrosion can occur.
I would open the phone and disassemble it as good as you can. Let every part dry. Also, take the motherboard in particular and lay it into isopropyl alcohol (90%). Let it stay there for about 10 minutes before you take it out of it. Then let it dry for about 2 days (e.g. next to a warm source like an air conditioning) before you put it back again.
Sure, water damage could have created an immediate shortcut. However, by following the steps above we might be able to solve the issue or - at least - are able to go from there.