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Xavi Fores has headed proceedings in the opening free practice session at Jerez on the Barni Ducati in front of Nicky Hayden and double winner from Magny-Cours Chaz Davies.
The privateer Ducati entry sneaked ahead in the closing stages of FP1 by ducking under Hayden's benchmark by one-tenth to go fastest with a 1m 42.008s.
Hayden, who has scored two podium results at Jerez in MotoGP, made a late improvement with a 1m 42.073s but couldn't topple the Spaniard at his home event.
Aruba.it Racing Ducati's Davies held on to third ahead of Althea BMW's Jordi Torres with Pata Yamaha's Alex Lowes enjoying a solid start to his race weekend in fifth.
Yamaha-bound Michael van der Mark narrowly missed out on topping 2017 team-mate Lowes in the closing minutes to finish the session sixth overall ahead of championship leader Jonathan Rea.
Leon Camier suffered a crash late in FP1 on the MV Agusta but held on to eighth spot on the final timesheet in front of the returning Anthony West as title contender Tom Sykes rounded out the top ten from Markus Reiterberger and Alex de Angelis.