Andrea Dovizioso led Ducati MotoGP stablemate Jack Miller by 0.009 seconds in a tight second practice for the Argentine Grand Prix.
First practice pacesetter Marc Marquez led for much of the session on his Honda, but was usurped by a late flurry of fast laps, with Qatar winner Dovizioso emerging fastest of all.
Marquez shot to the top of the timesheets straight away in FP2 with a 1:40.146s, but was briefly beaten by Pramac's Miller, who fired in a 1:39.920s.
Reigning world champion Marquez subsequently guided his Honda to the best lap of the day by just over a tenth from Miller, before improving to a 1:39.689s.
Running soft rear rubber early on, Marquez raised the bar further with a 1:39.497s with just under 15 minutes of the session gone.
Miller remained his closest challenger for some time, just as he did in FP1, but was over four tenths adrift. The Australian suffered a small tumble at Turn 13 in the early stages, but to no consequence.
As the session reached its closing moments, the timing screens were ablaze with session-best sectors, with Marquez's top spot put under considerable threat by Petronas Sepang Racing rider Franco Morbidelli.
He missed out by 0.006s, but Cal Crutchlow on the LCR RC213V managed to depose Marquez with a 1:39.346s.
This stood as the benchmark for all of a few moments, as Miller edged ahead with a 1:39.190s, before one-time Argentina podium finisher Dovizioso found a further 0.009s on his final lap.
Maverick Vinales brushed off his low-key morning performance to end the day third overall with a 1:39.345s, beating Crutchlow and SRT's Fabio Quartararo in the process.
Valentino Rossi shadowed his Yamaha stablemate in sixth, with Alex Rins [Suzuki] bumping Marquez – who did not run a fresh tyre at the end of the session – back to eighth. Morbidelli and Takaaki Nakagami [LCR] completed the top 10.
Danilo Petrucci was unable to mount a challenge for the top 10 in the closing moments, and had to settle for 13th on his factory Ducati ahead of Pramac's Francesco Bagnaia.
Jorge Lorenzo struggled in the second session, and despite being within nine tenths of Dovizioso's best lap, the injured Honda rider was second-to-last in 21st.
