Suzuki rider Andrea Iannone topped the opening day of MotoGP's Jerez test, edging out Cal Crutchlow by less than a tenth of a second.
This week's Jerez test, which runs from Wednesday to Friday, is being attended by the majority of MotoGP teams - with only Repsol Honda, Yamaha, Tech 3 and Aspar absent - plus a number of leading World Superbike and British Superbike squads.
Pramac Ducati did not take part on Wednesday, but is set to join the action on Thursday.
Iannone hit the top of the times shortly before noon, knocking Kawasaki WSBK star Tom Sykes off the top of the times with a 1m38.652s.
That stood as the benchmark until Ducati rider Jorge Lorenzo posted a 1m38.483s with a little under three hours remaining, although that was soon beaten by his teammate Andrea Dovizioso, who set a 1m38.398s.
It was just before the start of the final hour that Iannone retook the top spot, setting a 1m38.280s - coming within 0.031s of Dani Pedrosa's pole time from this year's Jerez race, which was held before the track was resurfaced.
Cal Crutchlow moved up to second aboard the LCR Honda on a 1m38.337s before a late crash for Ducati WSBK rider Chaz Davies at Turn 1 that caused a lengthy late stoppage with 30 minutes to go.
Dovizioso's time was good enough for third, ahead of Lorenzo and lead KTM rider Pol Espargaro, who also caused a red flag when he crashed at Turn 3 in the third hour.
Sykes's early benchmark meant he was the fastest WSBK representative in sixth overall ahead of Avintia Ducati's Tito Rabat and his Kawasaki teammate Jonathan Rea.
Bradley Smith (KTM) and Scott Redding (Aprilia) rounded out the top 10.
Sylvain Guintoli was in action for Suzuki, ending up 15th-fastest, while Eugene Laverty - standing in for Aleix Espargaro at Aprilia - was 16th.
Moto2 frontrunner Alex Marquez had his first taste of the Marc VDS Honda a day ahead of schedule, but ended the day down in 25th place, some 3.4 seconds off the pace.
Testing times (MotoGP only):