Hamilton narrows gap to faltering Ferrari
Lewis Hamilton suggested Ferrari had half a second over Mercedes on Friday before making a mockery of his own statement by almost wiping out the Scuderia's advantage.
Hamilton won his fifth drivers' championship last year, easing away from Sebastian Vettel over the course of the campaign.
But Vettel and Ferrari had initially been in scintillating form in pre-season, regularly running the fastest car in testing at the Circuit de Catalunya in Barcelona.
However, a seemingly dominant test took a turn on Wednesday when Vettel hit the barriers due to a mechanical issue that kept the car off the track for several hours.
There were further problems on Friday and Ferrari's week ended early as an electrical issue hindered Vettel.
That presented Hamilton with an opportunity, although the Briton had not been confident of Mercedes' early season hopes midway through the day.
"I think it's potentially half a second [to Ferrari], something like that," he had said, adding: "This is going to be the toughest battle yet, which is exciting for all the fans.
"Ferrari's pace is very, very good at the moment, so the challenge is going to be harder than ever."
His response was to set a best time of one minute and 16.224 seconds during his 61 laps, giving up just 0.003secs to the table-topping Vettel.
Silver Arrows team-mate Valtteri Bottas was a further 0.337secs back.
There were various other problems down the field. Max Verstappen completed just 29 laps for Red Bull before a gearbox issue ended his week, while Haas' Kevin Magnussen was halted at turn four.