Xavi Vierge snatched a maiden Moto2 pole position away from Lorenzo Baldassarri at the end of a wet Argentina qualifying.
The intensifying rain which truncated the preceding Moto3 session in the closing stages remained for the start of qualifying, with a number of riders venturing out on slicks quickly forced back into pitlane to switch to wet tyres.
Qatar podium finisher Baldassarri staked his claim for a maiden pole with an early effort of 1:58.076s, which he improved to a 1:56.408s having been briefly deposed by Mattia Pasini.
With only 10 minutes of the session gone, the rain fell slightly harder, though improvements were still being made by numerous riders, including championship leader Francesco Bagnaia, who was one a handful of runners who started the session on slicks.
The Sky VR46 rider improved from 16th to seventh with a 1:57.891s, while CBGM rider Sam Lowes jumped up to a provisional front row in third.
Baldassarri looked set to start from pole for the first time in his career as the chequered flag flew, but a last-gasp effort of 1:56.137s put Vierge almost three tenths clear of the field, while Danny Kent secured his first front row start since the 2015 Aragon Moto3 race.
Pasini found himself shuffled back to fourth in the end, while a late 1:56.679s put Gresini's Navarro into the middle of the second row ahead of Lowes.
Oliveira heads row three on the Ajo KTM, while Alex Marquez salvaged eighth after an early crash at the first corner. FP3 pacesetter Remy Gardner will start from ninth on the Tech3 machine.
Joe Roberts put the new NTS chassis tenth of the grid ahead of Kiefer Racing's Dominique Aegerter and the first of the Sky VR46 bikes of Luca Marini.
Marini's teammate Bagnaia will have work to do to maintain his standings lead after slipping to a lowly 15th behind Steven Odendal and Isaac Vinales.
Romano Fenati was left stranded in 19th on the grid after a lengthy spell in his Marinelli Snipers garage, the Italian only managing 10 laps after taking to the circuit in the closing 15 minutes.
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