GP2 newcomer Sergey Sirotkin posted the fastest time at the start of the second day of testing in Bahrain, delayed by an overnight sandstorm.
The morning session started an hour late as efforts were made to clean the circuit, and reduced to two hours of running.
Sirotkin claimed top spot in the dying minutes with a time of 1m41.797s.
The Russian was almost half a second ahead of his nearest challenger, day one pacesetter Jordan King. Alex Lynn made it three rookies in the top three.
Rio Haryanto was bumped from first to fourth at the end of the session, finishing just ahead of his Campos team-mate Arthur Pic, with the ART duo of Stoffel Vandoorne and Nobuharu Matsushita next up.
Julian Leal, Rene Binder and Alexander Rossi completed the top ten.
The sandy conditions led to only 18 cars setting times, with Status Grand Prix, Russian Time and Arden keeping their cars in the pits, while Dutch drivers Nigel Melker (Hilmer) and Daniel De Jong (MP Motorsport) were also absent.
Morning session results
|2||Jordan King||Racing Engineering||1:42.289||0.492||10|
|4||Rio Haryanto||Campos Racing||1:42.437||0.640||15|
|5||Arthur Pic||Campos Racing||1:42.483||0.686||21|
|6||Stoffel Vandoorne||ART Grand Prix||1:42.557||0.760||12|
|7||Nobuharu Matsushita||ART Grand Prix||1:42.588||0.791||14|
|10||Alexander Rossi||Racing Engineering||1:43.390||1.593||15|
|14||Nick Yelloly||Hilmer Motorsport||1:43.877||2.080||9|
|17||Sergio Canamasas||MP Motorsport||1:44.954||3.157||6|