Lewis Hamilton believes he needs to get his "act together" in order to prevent Nico Rosberg from claiming pole position for Sunday's German Grand Prix.
Hamilton will head into the Hockenheim race in charge of the championship for the first time this season following his victory in Hungary.
But the defending champion, who has won five of the last six races, was slower than home favourite Rosberg in both practice sessions on Friday.
Indeed Rosberg was comfortably quicker than Hamilton, with his best lap of one minute and 15.614 seconds in the second session nearly four tenths faster than that of his Mercedes team-mate.
"I hope I can get my act together tomorrow," said Hamilton. "It was just not a great lap, so I am not particularly worried.
"FP2 didn't feel very good. It got worse and worse with some balance issues, but I will rectify it for tomorrow.
"Overnight we should be in a good position, and tomorrow it should be close as Nico is pretty quick here. He is feeling quite confident and calm in the car."
Rosberg, a winner of the opening four races, is now on the back foot in his pursuit of a first championship, after seeing his healthy 43-point lead turn into a six-point deficit.
Indeed since their dramatic crash on the opening lap of the Spanish Grand Prix in May, Hamilton has taken 135 points from 150 available, while Rosberg has won only once.
But Hamilton, for whom the early part of his championship defence was blighted by a number of technical problems, insists he has not changed his racing approach.
''I've been driving exactly the same as I have in the previous part of the year, but just not had any gearbox failure or engine problems,'' Hamilton added.
''I am very much a believer in waves, and I've finally got on a good wave in the last six races. Hopefully the wave continues here.''
Formula One is back in Germany after a one-year absence, and it was here in Hockenheim where Michael Schumacher, the seven-time champion, triumphed on four occasions.
His son Mick Schumacher, 17, currently competing in the Italian Formula Four championship, was among the VIP guests in Hamilton's Mercedes garage on Friday.
"He was upstairs in the motorhome, so I went up and introduced myself," Hamilton added. "He is probably looking at us thinking I can beat them just like I did when I was his age."
Ferrari driver Sebastian Vettel was the best of the rest on Friday, finishing in third, albeit more than half-a-second adrift of Rosberg. The Red Bull duo of Max Verstappen and Daniel Ricciardo, who is celebrating his 100th grand prix start here, were fourth and fifth respectively.
Jenson Button, who was given the all-clear to race after he was taken to a nearby hospital with an eye complaint, was eighth fastest for McLaren. His team-mate Fernando Alonso finished 10th.
Jolyon Palmer, the British rookie who missed out on his first points finish in Formula One after spinning from 10th in Hungary, was replaced by Renault's French reserve driver Esteban Ocon in first practice.
Palmer returned to the cockpit on Friday afternoon, but was only 20th in the standings, three places and two tenths of a second shy of his Renault team-mate Kevin Magnussen.
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