Mercedes brought a raft of updates to Barcelona for the Spanish Grand Prix, but Hamilton said he was still struggling with the W13 car in qualifying, leaving him sixth on the grid.
Contact with Haas driver Magnussen on the opening lap caused Hamilton to slow and forced him into an early pitstop, leaving him over 50 second off the leader at the end of the opening lap.
Hamilton asked Mercedes over the radio if it would be worth saving the engine on his car, only to be told that he could still finish as high as eighth.
But Hamilton ultimately clawed his way back up to fifth at the chequered flag, having only lost fourth place to Carlos Sainz in the closing stages when a water leak forced him to slow down.
Hamilton explained that the race pace was "much better" and the car felt "much ni