Early pace setter
After a damp opening Free Practice session on Friday morning, dry conditions greeted the premier class riders in the afternoon sun. Wet weather is forecast to disrupt qualifying day, so FP2 could well decide who is heading into Q2 automatically.
Immediately, Captain America set the pace. Six-time COTA winner Marquez was half a second clear of Miller after 20 minutes of dry track time, with just seven riders within a second of the number 93 in the early stages.
Miller moves up
Miller then cut Marquez' advantage to 0.123s with just under 15 minutes to go, as soft Michelin tyres were then fitted for a mini Friday afternoon qualifying stint.
Second in the title race Francesco Bagnaia (Ducati Lenovo Team) and Takaaki Nakagami (LCR Honda Idemitsu) were the first riders to beat Marquez' time, the Japanese rider the faster of the two, as Miller then went P2 ahead of his team-mate.
Quartararo steps up
Quartararo then shot to P1 by over two tenths before Marquez - after slipping to the lower ends of the top 10 - returned to the top with another benchmark.
Miller threatened to take top spot but the Aussie's final lap was just shy and truly only just - leaving only 0.015sec separating the duo at the end of the day.
Nakagami in the mix
Behind the leading trio is Pol Espargaro (Repsol Honda Team), the Spaniard looking good in both wet and dry conditions at COTA, and with Nakagami fifth, it's a very promising opening day for Honda.
Bagnaia is in the mix in P6, the Italian just under half a second away from Marquez' time, with Pramac Racing pair Jorge Martin and Johann Zarco seventh and eighth respectively. 2019 Austin winner Alex Rins (Team Suzuki Ecstar) and Misano podium finisher Enea Bastianini (Avintia Esponsorama) complete a top 10 covered by 0.6sec.