MotoGP championship leader Marc Marquez moved to the top of the times in second practice at the Termas de Rio Hondo circuit in Argentina.
The Honda rider improved on his morning time by over six seconds, stopping the clock at 1m39.313s to finish over a second ahead of his closest rival.
Team-mate Dani Pedrosa finished second, ahead of the Aleix Espargaro, again the quickest of the Open class riders on the Forward bike.
LCR Honda's Stefan Bradl, one of the few men with previous experience of the track, was fourth ahead of Ducati's Andrea Dovizioso.
Practice one pacesetter Jorge Lorenzo finished down in ninth position, behind team-mate Valentino Rossi, the only current rider to have won a race in Argentina.
The times tumbled right away as the track conditions continued to improve, with Marquez beating the morning's benchmark by over two seconds with his second flying lap of the session.
Marquez went even quicker after the 45-minute session had reached the halfway mark, at which point the Spaniard was nearly a second clear of the field before Dovizioso improved and jumped to second on his return to action following early problems.
Dovizioso suffered an apparent engine blow-up less than 10 minutes into the session, his Ducati coming to a stop amid a big puff of smoke.
Marquez increased his lead with four minutes remaining, becoming the first man to lap in the 1m39s after a massive one-second improvement.
Andrea Iannone also had drama early on after losing control of his bike under braking at Turn 5.
The Pramac Ducati rider, who seemed to overshoot his braking point, walked away from the crash, but his bike was badly damaged. He would return to action later in the session.
Pos Rider Team Time Gap Laps
1. Marc Marquez Honda 1m39.313s 18
2. Dani Pedrosa Honda 1m40.396s +1.083s 18
3. Aleix Espargaro Forward Yamaha 1m40.566s +1.253s 16
4. Stefan Bradl LCR Honda 1m40.891s +1.578s 20
5. Andrea Dovizioso Ducati 1m41.042s +1.729s 11
6. Bradley Smith Tech 3 Yamaha 1m41.303s +1.990s 20
7. Pol Espargaro Tech 3 Yamaha 1m41.368s +2.055s 19
8. Valentino Rossi Yamaha 1m41.395s +2.082s 21
9. Jorge Lorenzo Yamaha 1m41.533s +2.220s 18
10. Andrea Iannone Pramac Ducati 1m41.924s +2.611s 13
11. Alvaro Bautista Gresini Honda 1m42.029s +2.716s 20
12. Yonny Hernandez Pramac Ducati 1m42.128s +2.815s 16
13. Karel Abraham Cardion Honda 1m42.348s +3.035s 18
14. Colin Edwards Forward Yamaha 1m42.608s +3.295s 19
15. Nicky Hayden Aspar Honda 1m42.621s +3.308s 18
16. Hector Barbera Avintia FTR-Kawasaki 1m42.739s +3.426s 16
17. Broc Parkes PBM Aprilia 1m42.827s +3.514s 14
18. Michele Pirro Ducati 1m42.898s +3.585s 17
19. Danilo Petrucci Ioda Aprilia 1m43.106s +3.793s 18
20. Mike di Meglio Avintia FTR-Kawasaki 1m43.125s +3.812s 14
21. Michael Laverty PBM Aprilia 1m43.151s +3.838s 17
22. Scott Redding Gresini Honda 1m43.165s +3.852s 16
23. Hiroshi Aoyama Aspar Honda 1m43.347s +4.034s 18