Yamaha's MotoGP championship leader Maverick Vinales set the pace in first practice for the Argentinian Grand Prix.
Fears the state of the little-used Termas de Rio Hondo circuit would cost riders meaningful running on Friday morning were eased early, with times quickly dropping into the 1m41s barrier.
Vinales' 1m41.469s set 12 minutes in was faster than the best time recorded across the two Friday practice sessions in Argentina 12 months ago.
Having moved into top spot, Qatar winner Vinales then had a violent near-highside - which prompted his airbag to go off on landing - coming through the final sequence of corners nearing the 15-minute mark.
Tech3 Yamaha rookie Johann Zarco grabbed top spot briefly with 20 minutes remaining, with a 1m41.258s, but Vinales quickly reasserted himself with a 1m40.796s that was 0.462 seconds clear of the pack.
Marc Marquez crashed at Turn 2 just before Zarco and Vinales upped the pace at the front, having lost the front end of his Honda, but the world champion headed back out on his second bike and cut that gap to 0.162s inside the final 10 minutes.
Vinales opted to fit the harder rear tyre for his last run - as many riders used the soft chasing a lap time - and improved twice again.
The Spaniard set a 1m40.385s with seven minutes remaining, and improved to 1m40.356s three minutes later.
That gave Vinales an advantage of 0.206s at the end of the 45 minutes of running.
He was followed by four satellite riders, who all improved in the closing stages; Danilo Petrucci on Pramac's 2017 Ducati, Zarco and his Tech3 team-mate Jonas Folger and Aspar Ducati's Karel Abraham.
Suzuki rider Andrea Iannone was sixth and 0.345s adrift, as the lead Ducati of Andrea Dovizioso, Avintia Ducati's Hector Barbera, Marc VDS Honda's Jack Miller and Aspar's Alvaro Bautista rounded out the top 10.
Marquez, who won in Argentina last year, did not improve in the closing stages and wound up 11th, ahead of Aleix Espargaro on the first of the Aprilias.
Jorge Lorenzo and Valentino Rossi were anonymous for the bulk of the morning, sitting 17th and 18th in the order before their final runs.
On soft tyres, that vaulted Lorenzo up to fifth and Rossi eighth, but they were ultimately bumped back down to 15th and 16th, with Rossi the last rider lapping within one second of Vinales.
Riding with an injured right ankle, Suzuki rookie Alex Rins was 17th, while Pol Espargaro led the way for KTM in 20th, 1.473s off the ultimate pace.
After Michelin's rear-tyre dramas in Argentina last year, its second weekend back in MotoGP, all riders have been instructed to complete five timed laps on the hard rear tyre in either of Friday's practice sessions.
Ten riders managed that in first practice, and any of the remaining 13 who fail to meet the requirement will be dealt a six-place grid penalty for Sunday's race, unless the second session is affected by wet weather.
PRACTICE ONE TIMES: