Mattia Pasini headed Miguel Oliveira on the Moto2 standings in Argentina on a Friday affected by rain in the afternoon.
The opening session for the Argentina weekend was a frantic affair, with top spot changing hands frequently to the chequered flag.
Last year's Argentina polesitter Oliveira looked set to top FP1 with a late effort of 1:44.633s, but the Ajo KTM rider was pipped by Italtrans' Pasini at the death with a 1:44.461s.
Qatar race winner Francesco Bagnaia completed the top three having been an early pacesetter, while Oliveira's teammate Brad Binder and SAG Racing's Isaac Vinales rounded out the top five at the end of FP1.
Binder and Oliveira swapped fastest lap at the start of the second session, the latter leading the way with a 1:44.805s.
Alex Marquez edged 0.003 seconds ahead of the Portuguese rider 10 minutes into the session, and remained top of the FP2 timesheets thanks to the arrival of rain with 20 minutes of the afternoon outing remaining.
Pasini was only seventh in the second session, but his FP1-topping time remained unchallenged in the afternoon, with only five of the 32-strong field – including Marquez – improving on their best efforts from the morning.
Oliveira, Bagnaia and Binder remained where they were at the end of FP1 on the combined times, while Vinales found himself shuffled back to sixth courtesy of Marquez's improvement.
Speed Up's Danny Kent ends Friday seventh overall ahead of Jorge Navarro, Xavi Vierge and Remy Gardner – the latter two the only ones inside the top 10 to improve on their FP1 bests.
Joan Mir – who won last year's Moto3 race in Argentina – was just 0.010s from the top 10, with Sam Lowes and Qatar podium finisher close behind.
Jules Danilo [32nd] was one of two crashers on Friday, the Moto2 rookie falling at Turn 13 at the end of FP1. Fellow Moto3 graduate Bo Bendsneyder [25th] also took a tumble at the penultimate corner just moments later.
