Lap times improved dramatically in the hour-long afternoon session compared to FP1 earlier today, with Martin blasting the lap record set by Francesco Bagnaia last year of 2m01.892s with a 2m01.397s.
The Pramac rider, who leads the standings by 18 points, beat FP1 pacesetter Maverick Vinales on the factory Aprilia by 0.076 seconds.
Seven-time COTA race winner Marc Marquez was third with a late 2m01.806s on his year-old Gresini Ducati, as Bagnaia lifted himself into Q2 safety late on in fourth.
Martin set the initial pace in second practice with a 2m04.429s, which was instantly beaten by Ducati’s Enea Bastianini with a 2m04.208s.
Pedro Acosta followed this up with a 2m03.578s on his Tech3 GasGas, before Martin edged clear seconds later with a 2m03.036s inside the first 10 minutes of the session.
This would stand as the benchmark for the next 20 minutes until Vinales, his Aprilia fitted with a new soft rear tyre, fired in a 2m02.983s.
Martin followed close behind, though, and re-established himself at the top of the timesheets with a 2m02.888s.
Maverick Vinales, Aprilia Racing Team
Photo by: Gold and Goose / Motorsport Images
Another 15 minutes passed before Vinales once again took top spot away from Martin with a 2m02.394s, which was followed up by a 2m02.244s from VR46 Ducati rider Fabio Di Giannantonio.
But Martin was blowing up the timing screens behind this duo and flashed across the start/finish line with just under 13 minutes remaining with a new lap record of 2m01.397s.
Vinales was the only rider to put this time under threat on his final time attack lap but came up 0.076s short with a 2m01.473s.
Marc Marquez completed the top three with a final lap of 2m01.806s, while Bagnaia ended the session fourth having sat outside of the Q2 places in 12th as second practice entered its closing moments.
Acosta completed the top five and is the only KTM rider inside the Q2 places at the moment, with factory counterpart Brad Binder the next-best RC16 in 14th – 0.585s adrift of the 19-year-old rookie.
Aleix Espargaro was sixth on the sister factory team Aprilia, as Franco Morbidelli bagged his first Q2 appearance as a Pramac Ducati rider.
Bastianini, Di Giannantonio and his VR46 team-mate Marco Bezzecchi rounded out the top 10.
Miguel Oliveira and Raul Fernandez narrowly missed Q2 places for home team Trackhouse Racing’s first Americas GP, while Fabio Quartararo was the leading rider for a Japanese brand in 17th on his Yamaha.
A crash for Joan Mir at the end of the session left him in 20th, with LCR Honda’s Johann Zarco the leading HRC representative in 19th.
