"Obviously, both cars have got bits that they (the engineers) are having a look at for future events", said Horner.
The sister pink vehicle was driven extremely well to 12th place by rookie George Russell, having his first official F1 run at a Grand Prix meeting; the GP3 champion lapped only six-tenths slower than Ocon despite never having seen Interlagos before.
He has now sensationally claimed that he would allow Valtteri Bottas to win the Grand Prix this weekend, but only if Mercedes asked him.
Red Bull's Mexican GP victor Max Verstappen was the only driver to set a laptime in the first 10 minutes - but his initial benchmark was quickly surpassed by the soft-shod Mercedes of Bottas, the Finn ending his first run on a 1m10.102s laptime.
The Dutch 20-year-old has now won two of the last four races, after a run of poor reliability, while Red Bull have scored more points than second-placed Ferrari since the end of the August break. "As a team we really want to finish one and two". "We're in a decent position but I think it could be quite close".
"I don't think they are going to ask", Hamilton said when asked if he would follow team orders to allow Bottas to pass.
"There are still two races to go".
Mercedes have clinched the constructors' championship for a fourth successive year and experimented with processes and parts for 2018.
Red Bull's Max Verstappen was third, 0.433s off the pace with Kimi Raikkonen three tenths further back in fourth.
Daniel Ricciardo finished fifth fastest, though is set to be handed a 10-place grid penalty after taking on a new MGU-H, his eighth of the campaign.
Finnish team mate Valtteri Bottas is third overall and only 15 points behind Ferrari's Sebastian Vettel, a four-times victor this year, with Mercedes determined to finish one-two for the fourth season in a row.
"I'm not expecting anyone to completely ruin his race for me, so as I said it all depends on the situation".
Sergio Perez was 12th for Force India ahead of Stoffel Vandoorne, while Williams rookie Lance Stroll finished in 14th, though he will hope to cut the 0.7s deficit to teammate Massa in qualifying.