The match at Orlando City Stadium was delayed by an hour after a thunderstorm soaked the surface, but once play began England were sharp, purposeful and increasingly fluid as the game progressed.
Rice opened the scoring when Gordon broke down the left flank, reached the byline and pulled the ball back for the West Ham and Arsenal central midfielder to sweep a first-time left-footed effort into the bottom right corner.
Gordon, starting on the left in the absence of a fully fit Bukayo Saka, then doubled the lead from the penalty spot after Eberechi Eze's shot struck an arm inside the area. Gordon stepped up with Harry Kane off the pitch and drove a confident effort into the top corner.
Watkins came off the bench to add a late third, heading home from close range after Morgan Rogers's curling attempt was parried into his path by the Costa Rica goalkeeper.
England's head coach spoke to ITV after the final whistle and was direct in his assessment.
"We saw very good substitutes, who, of course, were disappointed not to start, but to come in and to play with the same intensity and quality against a more tired opponent. What we see today was exactly what we wished for and exactly what we wanted. Very proud. Next stop, Kansas."
Tuchel declined to confirm his starting XI for the Croatia opener.
"No. I have another six days I think."
He outlined the schedule between the two games.
"First of all, we do a match tomorrow. Another friendly match to get minutes into the players who didn't play today. Then the players get one and a half days off to switch off physically and mentally. Change location, go to Kansas and then prepare for Croatia."
Rice, who spoke with obvious satisfaction after the result, noted the evolution of the squad's understanding during the tournament preparation.
"I think we've adapted. You can see the heat is not really a problem now. I think the first week, ten days has been adapting to the heat. Playing with him and Nico, we were speaking all week about how we're going to play, rotate, be fluid. You see that in the first half and you see as a group now we're building confidence, fitness and going into that first game now we've got more training sessions. We're going to keep building and it's really good."
Gordon, who impressed from first minute to last, was buoyant after scoring from the spot.
"There is always pressure when you play for England. As you know, there is top players behind you waiting on the bench to come on. There is always pressure. If you can't deal with that, you're at the wrong level."
He admitted he had been looking for the penalty responsibility.
"I was buzzing H was off. I was looking around to find him. When he was off I wanted to take it. I love penalties and I love the pressure of it. Glad to see that one go in."
England face Croatia in Kansas City on June 17. Tuchel's squad goes into the tournament on the back of three wins from three warm-up fixtures, with a performance level here that offered genuine grounds for optimism.
The tournament starts next week. The preparation is done.