Mercedes director of trackside engineering Andrew Shovlin has insisted the team "won't get excited" about a potential challenge to Ferrari and Red Bull despite a promising start to the Miami Grand Prix weekend.
George Russell finished second in first practice at the Miami International Autodrome, just 0.071secs down on F1 championship leader Charles Leclerc.
Crucially, the Briton was able to set his time at a similar point of proceedings to the Ferrari driver ensuring there could be no excuse regarding track evolution.
Asked if the team was back in the game after FP1, with Lewis Hamilton also competitive, Shovlin told Sky Sports F1: "I am not going to say that just yet.
"It has been an encouraging start to the weekend. We have got quite a lot of new parts on the car, new wings front and rear.
"We are always trying to get weight out of the car, we are still overweight and it looks like it seems to be working reasonably well.
"In Imola, we were struggling for warm-up, here it is overheating. Whether that has shifted us in the right direction I don't know but we won't get excited about where we are here.
"We know we should have improved the car but we know we have got a lot of work to do."
Mercedes "don't yet fully understand" porpoising variation
A striking difference in the W13's performance was the lack of porpoising that has plagued Mercedes' progress in the first four races.
But insisting the team was unaware as to why the bouncing had improved, Shovlin explained: "There is less but when we have gone from track to track, you get different amounts and we don't yet fully understand why, for instance, Jeddah seemed worse than Bahrain.
"We are still building up a picture of that but it does seem to be working quite well here.
"It isn't the issue it was in Imola but in Imola, just the one session to set the car up worked against us because this is not an easy car to position the set up at the moment."
Mercedes upgrades explained
In the upgrade package Mercedes has introduced, new front wing endplates, rear wing and beam wing are the highlights in the search for improved performance.
The front wing in particular is a departure from the initial component, with aggressive cutaways from the end-plates seemingly aimed at providing a greater outwash effect around the front wheels.
"That is going to affect the flow down the car and elements like the outwash but fundamentally though, it is just more downforce for the same drag and the rear wings are more efficient wings than the ones we have been running," said Shovlin.
"At low drag tracks, we have trimmed our wings away, this one is designed for the downforce so both of those together are useful.
"As I said, these are items that when we remake them, we make them lighter to help us get more weight out of the car."