Lewis Hamilton raised the bar for this week's Spanish Grand Prix by setting the fastest time in second practice on Friday.
Hamilton was beaten to top spot by his Mercedes team-mate Valtteri Bottas in the opening running, but the reigning champion ended the day fastest at Barcelona's sun-bathed Circuit de Catalunya.
The British driver's best effort of one minute and 18.259 seconds enabled him to edge out Daniel Ricciardo by less than two tenths with his Red Bull team-mate Max Verstappen third.
Ricciardo crashed out of opening practice earlier on Friday after he lost control of his Red Bull at Turn 4 and slid helplessly across the sand trap and into the barriers.
But following repairs to his car, the Australian, backed up by Verstappen, ran Hamilton close to suggest Red Bull have the credentials to take the fight to Mercedes and Ferrari.
Ferrari rarely show their true pace on Friday and Sebastian Vettel, who trails Hamilton by four points, finished in fourth, a third of a second down on Hamilton's best time.
Vettel's team-mate Kimi Raikkonen posted the sixth fastest lap, but was told to park his Ferrari after puffs of white smoke came from his engine. Bottas was fifth in the order.
FP2 CLASSIFICATION@LewisHamilton on top, with @redbullracing breathing down his neck
— Formula 1 (@F1) May 11, 2018
This could get interesting 👀#F1 🇪🇸 #SpanishGP pic.twitter.com/y0TkWzFVnq
Mercedes, Ferrari and Red Bull have all brought revised cars to this weekend's race with the opening western European round of the season traditionally kick-starting the development war.
And Bottas's early pace - the Finn posted a record-breaking lap of this 2.9-mile track - followed by Hamilton's time in the second session, would indicate Mercedes have taken the greater stride forward with Vettel's Ferrari team having previously boasted the most complete package of the season.
McLaren had also been hopeful that their revised car would curb a downward spiral, but after Fernando Alonso finished a dizzying sixth by trading times with the Red Bull cars in the day's opening running, he was only 12th in the afternoon session.
Saturday marks the fifth anniversary of the Spaniard's last victory in F1, and it is highly likely that he may never win again.
Stoffel Vandoorne was ninth, but there is still significant work to do for the British team, who have failed to get either of their cars into the final phase of qualifying this season.
Robert Kubica is back competing at his first grand prix weekend in more than seven years after suffering career-changing injuries to his right arm in a rally crash.
The Pole, now acting as reserve driver for Williams, was last but one in the opening sessions, 1.3secs ahead of team-mate Lance Stroll.
Lewis Hamilton had to settle for second place in opening practice at the Spanish Grand Prix as his Mercedes team-mate Valtteri Bottas lit up the time sheets.
Bottas, who has out-qualified Hamilton at four of the past six races, held the advantage once more with a record-breaking lap of Barcelona's Circuit de Catalunya.
The Finn's flyer of one minute 18.148 seconds enabled him to finish the best part of nine tenths clear of Hamilton with Ferrari's Sebastian Vettel third in the order, and the only other driver within one second of Bottas.
Bottas earlier spun at Turn 13, while Vettel, who trails Hamilton by four points in the championship, also came unstuck at Turn 10 in a session notable for incidents.
Red Bull's Daniel Ricciardo was the biggest casualty after he lost control of his Red Bull at Turn 4, took a trip across the gravel, and thudded into the barriers.
The Australian's session was instantly over as he hitched a lift to the pits and his damaged car was taken on a truck back to the Red Bull garage for repairs.
The Mercedes pair lead the way in FP1 morning in Barcelona
— Formula 1 (@F1) May 11, 2018
As Kubica beats his teammate on his Grand Prix weekend return 💪#F1 🇪🇸 #SpanishGP pic.twitter.com/BsDVR0p12Q
Mercedes, Ferrari and Red Bull have all brought revised cars to this weekend's race with the opening European round of the season traditionally kick-starting the development war.
Bottas's early pace suggests Mercedes may have taken a positive stride forward with Vettel's Ferrari team having previously boasted the most complete package of the season.
Kimi Raikkonen was fifth, 1.3secs adrift of Bottas, with the Red Bull duo of Max Verstappen and Ricciardo, who managed to get in a competitive lap before his session-ending crash, fourth and seventh respectively.
Fernando Alonso finished sixth. McLaren, who have struggled this season despite moving from Honda to Renault engines, have also brought a series of upgrades to Spain.
Although it is only the early phase of the weekend, they will be encouraged to have seen Alonso trading times with the Red Bull cars. His team-mate Stoffel Vandoorne was ninth in the running.
Robert Kubica is back competing at his first grand prix weekend in more than seven years after suffering career-changing injuries to his right arm in a rally crash.
The Williams reserve driver was last but one in the running, 1.3secs ahead of his team-mate Lance Stroll, who finished last.