Mercedes has no answer on Miami GP performance loss
However, neither driver was able to repeat that sort of form from Saturday onwards, as other teams were able to extract more pace from their cars. They eventually finished Sunday's race in fifth and sixth places, with Russell ahead of Hamilton.
Russell complained that porpoising into corners had been a particular problem at the Florida track.
When asked about the performance loss across the weekend Elliott conceded that Mercedes was at a loss to explain it.
"That's a really good question and it's a question that we are trying to answer at the moment," he said in a Mercedes video debrief.
"I think if you were to look at Friday's running it was probably the most competitive we've been at any point through the season so far.
"Between Friday and Saturday we will have made some changes and actually those changes were fairly minor, but there were also changes in conditions and we need to go through all of that data, extract as much understanding as we can from that and use that to move forward over the next couple of races."
Elliott noted that efforts to control porpoising are progressing in parallel with the already planned performance development programme.
The front wing updates brought to Miami as part of the latter worked as intended.
"I think it is important to differentiate two things," he explained. "One is the normal upgrade path and the other one is fixing the issues that we are having with bouncing and other things that are compromising the performance.
"So, the wings that we brought definitely brought us the performance that we were expecting and were a step forward.
"The experiments we were doing on track trying to understand the bouncing, we gathered a lot of data, we gathered a lot of data on Friday when we had strong performance and we gathered data through the race and as always, the engineers are pouring through that, gaining understanding.
"In fact, every time we run the car we learn something new and that is the aim of the game, the game is to try and understand the car faster than our competitors."
Elliott stressed that a lot of activity is ongoing at the team's Brackley base to improve the W13.
"Although at the moment we are on the back foot a little bit with that, there is a huge amount of effort, a huge amount of work going in trying to understand how we improve the car, how do we find that next little step forward, how do we get rid of the bouncing and how do we get back to being competitive or competitive relative to the front-running team, which is where we want to be," he added.
Reflecting on the race, he also noted that Hamilton's car wasn't damaged in the first lap contact with Fernando Alonso in Miami.
"The contact was wheel-to-wheel and as always, we have lots of engineers looking at the data that is pouring off the car," he said.
"So the aerodynamicists are looking at pressure taps on the floors and wings, they are looking at the push rod loads and our chief engineer will be looking at all the other suspension loads and making sure that they are doing what they are supposed to be doing.
"So, we can very quickly tell whether there is an issue with the car and there was no issue to find."