Team Parker Racing's Porsches driven by Scott Malvern and Seb Hopkins set the GT3 and GT4 pace in opening practice at Donington this morning.
Just two hundredths of a second separated the top-two overall, and a second covered the first 10, while Hopkins recorded not one but two benchmark GT4 times.
Ulysse De Pauw, who joins RAM's #15 entry for the first time this weekend, made an instant impression on his series debut by topping the times after 10 minutes. However, Malvern - who was running second at that stage - unleashed a 1m26.653s just before one-third distance to put two tenths between himself and the Mercedes-AMG.
The Porsche's time was just over a tenth shy of British GT3's qualifying lap record and well under the race benchmark.
Last year's Donington winner, Marcus Clutton, moved Enduro's McLaren up to second moments later by lapping just 0.023s shy of Team Parker's 911, which spent the rest of FP1 piloted by Nick Jones.
A lull through the middle of the 60-minute session gave way to several more fast times in the final 20 minutes.
James Dorlin (Redline Racing, Lamborghini) was the first to move up the order, initially to sixth and then fifth thanks to consecutive quick laps, before Adam Carroll's Balfe-run Audi made it as many different manufacturers in the top-four.
The joint-championship leader finished 0.3s shy of the ultimate pace and eleven hundredths faster than Lewis Proctor who vaulted Greystone GT's McLaren up to fifth with four minutes remaining.
Lewis Williamson's PB just before half-distance helped 2 Seas' Mercedes-AMG to complete the top-eight ahead of Redline, RAM's second Mercedes-AMG, WPI's Lamborghini and Barwell's Huracan which topped the times early on.
Further back, two quick laps from Sennan Fielding saw Steller's Audi occupy GT4 top spot for the first 10 minutes despite the best efforts of Darren Turner who went around one-hundredth of a second slower in Newbridge's Aston Martin.
Academy's Mustang piloted by Matt Cowley was also in early contention just over a tenth further back, but it was Hopkins who ultimately emerged as the session's standout driver not once but twice.
His first flying lap put 0.137s between TPR's Cayman and Steller's R8 before a subsequent effort much later in the session lowered FP1's best to 1m35.041s.
Matthew Graham, whose Valluga Porsche occupied fifth at that point, pegged Hopkins back soon after, but his best was still 0.138s shy of the 16-year-old.
Theirs were the only changes of note after the first 15 minutes. Fielding's early time remained fast enough for third and a little under two tenths shy of the fastest Cayman, while Turner and Cowley also remained in a top-five covered by 0.4s.
Century's #90 BMW finished sixth, albeit a further half-second behind and just 0.06s ahead of Assetto's Ginetta. Toyota Gazoo Racing UK's Supra rounded out the first eight.
Free Practice 2 begins at 12:10 BST.