Fabio Di Giannantonio topped a damp final Moto3 practice ahead of qualifying for the Argentine Grand Prix, with Enea Bastianini 0.167 seconds adrift in second.
Overnight rain left the 2.99-mile Termas de Rio Hondo damp for the find lightweight class practice session. With the weather forecast unpredictable for the rest of the weekend, much of the field took to the circuit at the start to learn the conditions.
Home hero Gabriel Rodriogo set the initial benchamrk on his RBA Racing KTM with a 2:03.788s, before Gresini's Fabio Di Giannantonio deposed him with a 2:03.359s.
Prustel GP's Marco Bezzecchi – who scored his only grand prix podium in the wet in Japan last year – traded top spot with Di Giannantonio, with the latter regaining the upper hand with a 2:00.746s to go almost a second clear of the field.
Di Giannantonio's advantage was chipped away at, but no one was able to challenge the Italian's position. A final effort of 2:00.315s secured the Gresini man top spot, while Leopard's Bastianini leaped up to second at the end.
Bezzecchi was shuffled back to third courtesy of Bastianini's improvement, while Tatsuki Suzuki – who is still recovering from a hairline fracture on his arm sustained in a crash in Qatar – ended the morning fourth.
Aron Canet completed the top five, but was denied the opportunity to improve after his Estrella Galicia 0,0 Honda stopped at Turn 1 on his final lap.
Rodrigo, Friday pacesetter Jorge Martin, Adam Norrodin and Dennis Foggia completed the top 10, with Foggia's fellow rookie Alonso Lopez 0.034s further back in 11th ahead of Lorenzo Dalla Porta.
The conditions caught out CIP's John McPhee [25th] and SIC58's Niccolo Antonelli [20th], the former coming off at Turn 1 midway through the session, with Antonelli falling at Turn 13 in the closing stages.
