Vale dominated early on but ended up with nothing.
Sinnott said: "I thought we were the team in the ascendancy for the first 45 minutes. This was against a very good team in Swansea.
"But goals change games and change the mental psyche of teams. You only had to see once Swansea got their noses in front - they were like a peacock with its feathers. They were very efficient.
"You have to take your opportunities when they come along, but never more so than against a team at the top of the league."