Lewis Hamilton was beaten to top spot by Mercedes team-mate Valtteri Bottas on his return to action in Abu Dhabi.
The seven-time world champion was sidelined from last weekend's Sakhir Grand Prix after he contracted coronavirus.
But following 10 days of quarantine in Bahrain and after returning a number of negative swabs, Hamilton was back in his world championship-winning cockpit for the final round of the Formula One season, finishing 0.203 seconds behind Bottas.
The 35-year-old temporarily went faster than his team-mate only to see his speediest lap chalked off by the stewards after he exceeded track limits at the final corner.
It would appear a straight shootout for victory between the drivers of the sport's all-conquering team with Max Verstappen a distant third – almost eight tenths behind Bottas – while his Red Bull team-mate Alexander Albon was the only other driver to be within one second of Bottas' best lap.
There was drama late in the concluding action of the day as Kimi Raikkonen's Alfa Romeo caught on fire.
The 2007 world champion pulled off the track and coolly emerged from his cockpit before helping marshals to extinguish the flames.
The session was red-flagged for a dozen minutes as Raikkonen's chargrilled car was moved to safety.
Hamilton flew here from Bahrain on Thursday, and was given the all-clear to participate after Abu Dhabi officials provided him with an exemption despite strict Covid-19 protocols.
Yas Island has effectively been placed on lockdown since 10 charter planes touched down on Monday, with entry only permitted to those working at the season-ending race.
In Hamilton's absence at the penultimate round, George Russell was handed the keys to his compatriot's cockpit.
Russell, 22, finished ninth after he was robbed of victory twice – first following a Mercedes pit-stop howler and then a late puncture.
But after spending last weekend fighting at the front, it was back to reality for Russell in Abu Dhabi, after he finished 18th in his uncompetitive Williams machinery, 2.5secs slower than Bottas.
Earlier, Mick Schumacher, who secured the Formula Two championship in Bahrain last weekend, was handed his grand prix debut in first practice.
The 21-year-old German is set to follow in the footsteps of his father Michael Schumacher by competing on a full-time basis with Haas in 2021. He finished 18th of the 20 runners, almost four seconds off the pace.
The Yas Marina Circuit plays host to the 17th and final round of the Covid-disturbed campaign, as Hamilton bids to see out yet another championship-winning campaign with his 12th victory.
