Alex Morgan scored five goals as the world champions notched the biggest win in the tournament proper's history and sent a message to their rivals in the process on Tuesday.
Thailand were exceptionally poor, though, and Ellis acknowledged USA still have work to do if they are to retain their title in France.
"We're going to sit and look at some film. There's always things you can refine and polish," Ellis said.
"I'm not sure exactly what our next opponent [Chile] will do but teams sit low and it invites us on top of them a lot.
"It [this win] is how you want to start a tournament. You want to have that [winning] feeling.
"It's having players feeling good about the game. It is about building momentum, getting that first game under your belt – that feeling – that's going to be the biggest takeaway for us."
Ellis said she would have no problems keeping her players grounded, either, "because they are on a mission".
"This is one step in that. They understand that the mission matters most," she said.
Ellis understandably reserved special praise for five-goal hero Morgan and said it was "respectful" for her team to keep attacking until the final whistle, something they certainly did, scoring six times from the 74th minute.
"Alex tonight – I thought she was tight and tidy in the box. I thought she pulled the trigger well and again, [produced] some world class finishes," she added.
"That feeling – it's a self-belief, it's a confidence, it's an energy – call it what you want but goalscorers have to feel that. When you have a deluge of goals like that, it's a good feeling.
"Every team that is here has been fantastic to get to this point. To be respectful to opponents is to play hard against them. It's a tournament where goal differential is a criteria."