Jonathan Rea, who is aiming to wrap up his sixth successive World Superbike title this weekend and in the process record an unprecedented 100th win in the series, ended day one in fourth position on the time sheets on what is his first visit to the Estoril Circuit in Portugal.
Needing just three points for the crown, which could come in Saturday's opening race, the Ulsterman put in 39 laps as he familiarised himself with the circuit and was half a second slower than provisional pole man and Championship rival Scott Redding.
It has been 27 years since Estoril hosted the World Superbike Championship but Redding used his circuit knowledge from his Grand Prix days to take advantage after day one,
He is less than a tenth of a second ahead of Toprak Razgatlioglu, with Loris Baz - who crashed in the first session - third fastest and 0.4 seconds ahead of Rea.
Eugene Laverty, who also rode the circuit twice before in his 250cc Grand Prix career, was down in 18th position. He said: "It was that long ago that I had to treat today like a brand new circuit. This final round has crept up on us after a flurry of races in the past couple of months.
"We can be proud of our clear progress recently, pole position at Magny Cours, and I'm confident that we'll continue up the rankings this weekend."
Meanwhile, at Brands Hatch yesterday, Glenn Irwin got his British Superbike Championship quest off to a solid start by putting his Honda Fireblade in third position after opening practice.
Jason O'Halloran was fastest, 0.076 seconds ahead of the SYNETIQ BMW of Bradley Ray, who had a tenth of a second in hand over the Carrickfergus rider.
O'Halloran's team-mate Tarran McKenzie managed only seven laps before launching his McAms Yamaha over the barriers and into the undergrowth at Stirling's.
Mackenzie was unscathed, but the R1 will need engineers to burn the midnight oil to get it ready for Saturday.
Andrew Irwin was seventh fastest behind the Ducatis of Josh Brookes and Christian Iddon with half a second covering the top seven.
With five riders in contention for the BSB title this weekend, racing is sure to be competitive on the Brands GP circuit.
Korie McGreevy was best of the locals in the Supersport class in seventh position after his two sessions with Lee Johnston ninth and Richard Kerr 11th, while Alastair Seeley was eighth fastest of the GP2 machines.
Donegal brothers Rhys and Caolan Irwin went one-two in the Superstock 600cc combined practice with Randalstown's Eugene McManus third, Simon Reid fifth and Adam McLean ninth.
Keith Farmer, reverting to the Superstock 1000cc Championship this weekend, was sixth fastest overall with road racers Davy Todd, Ian Hutchinson, Michael Rutter and Conor Cummins 13th, 14th, 19th and 29th respectively.
BSB bosses revealed a provisional 11-round 2021 calendar yesterday with a new format that will see a series of UK tests prior to a later start to the season, which launches for the first time at Oulton Park on May 1-3.
The Mondello Masters round scheduled for Mondello Park this weekend has been cancelled.