Red Bull team principal Christina Horner was happy to see Max Verstappen come out on top over the two Mercedes drivers after Friday's free practice sessions at the Autódromo Hermanos Rodríguez.
But he remained concerned that Mercedes hadn't been showing their full potential so far, and that there was a lot more more to come from them heading in the Mexico City Grand Prix this weekend.
"Mercedes have still got a bit in their pocket, so I don't think we've seen their full potential yet," he told Sky Sports F1 at the end of yesterday's track activity.
Horner hinted that he had solid data to support his suspicions.
""During the session we have a bunch of analysts back in Milton Keynes," he explained. "You can see from the GPS overlays when they turn up the engine and when they turn it down.
"They'll be doing the same to us," he acknowledged. "So you can monitor what they have in the pocket and what they don't have."
On paper, the venue should work to Red Bull's strengths with the Honda engine working better in the high altitude conditions, and the RB16B's high rake angle making it possible to run higher downforce settings.
"The engine's working well at this altitude," Horner confirmed. "We're running Monaco wings, but have Monza downforce because of the thinness of the air up here.
"We found a reasonable balance today," he added. "It's a track that has suited our car over the last few years.
"But we've seen all year there's been less than a tenth between the cars, and we're expecting that to be the case [again in qualifying]."
But as for how things had gone so far, Horner couldn't hide his satisfaction after topping Friday's practice despite an early setback when Sergio Perez damaged his rear wing in a spin during FP1.
"It was a solid session for us," he said. "Both drivers are starting to find a setup to their liking. The short runs and the long runs look reasonable.
"[We are] focusing on ourselves, it was a reasonable day."
Gallery: The beautiful wives and girlfriends of F1 drivers
Keep up to date with all the F1 news via Facebook and Twitter
