Rosberg joins select group but title is the target

By Alan Baldwin SOCHI, Russia (Reuters) - Nico Rosberg joined an ultra-select group of Formula One drivers with his seventh win in a row for Mercedes at the Russian Grand Prix on Sunday but the German will remain the odd man out for some time yet. Only four drivers since the championship started in 1950 have won seven races in a row and only four have triumphed in the first four rounds of a season. Just one, Rosberg's compatriot Sebastian Vettel, has won more than seven in a row -- nine for Red Bull in 2013 when he won his fourth championship. All, bar Rosberg, were title winners but he is well on the way with a 43-point lead over triple champion, team mate Lewis Hamilton, who suffered power unit problems in both qualifying and the race, with 17 races remaining. "It sounds cool. But beyond that it's not my focus," Rosberg said when asked about the streak that started in Mexico last November. "It's great stuff but I just enjoy winning and I enjoyed winning today. "Of course it's not something I could have expected, to start the season with four. But now that's the way it is and I'm very happy about it. It's been a great four races, very enjoyable. "I'm aware it's not going to continue like that forever. Sport is always about up and downs and the down will come at some point," he added. "I just need to mentally prepare for that to then come straight back up when it does happen." That moment might almost have come in Sochi on Sunday, according to Mercedes motorsport head Toto Wolff, even if Rosberg gave every impression of enjoying a sunny afternoon drive in the Olympic Park. Wolff told reporters that data from the power unit on Rosberg's car "gave us some grey hair" during the race. "It looked at a certain stage that he wouldn't finish the race," added Wolff. Rosberg did not mention the problem on the podium or during a subsequent news conference, when he said the car was "fantastic" and he had driven flat out to the finish with plenty of life in the tyres. Asked about it later, the German conceded that he had lost "a fair chunk of performance" but Hamilton openly questioned that. "He was worried he wouldn't finish? As far as I'm aware, he didn't have a problem that was going to stop him finishing," said the Briton, who finished runner-up 25 seconds behind. (Reporting by Alan Baldwin, editing by Ian Chadband)