MANAMA, Bahrain - Nico Rosberg's downwards spiral has only worsened in Bahrain.With team mate Lewis Hamilton riding a wave of form and confidence, Rosberg headed to Bahrain determined to bounce back. But it backfired spectacularly in qualifying, as the 29-year-old slumped to third place, behind not only Hamilton but also Sebastian Vettel's resurgent Ferrari.GAP IS WORRISOMEHamilton won the Bahrain Grand Prix for the second year in a row, with Ferrari's Kimi Raikkonen back on the podium to deny Mercedes another 1-2 finish.Hamilton's pole-to-flag victory was his third win in four races this season and 36th of his career.Mercedes team chairperson Niki Lauda told Bild am Sonntag newspaper: "The starting point for Lewis is perfect as always. "But the six tenths gap between Nico and Lewis is worrisome," he added.On German television RTL, however, Lauda insisted Rosberg cannot be written off.But "from the first race in Melbourne, Lewis has simply done everything better. Nico needs to turn this around now."He needs to think about the counter-strategy he can do. It's not just about going faster, but thinking about something new to try to beat him," Lauda added.NOT GOOD FOR HIMThe F1 legend said Rosberg is also psychologically weaker at present, having erred in complaining about Hamilton's race tactics in China a week ago."Basically, Nico has realised that complaining after the race was not good for him," he said. "On the other hand, Lewis' answer was correct when he said 'I'm here to win the race'."So for now, F1 2015 appears headed for a two-horse title race, with the protagonists - silver-clad Hamilton and Vettel in the red corner - on the front row on Sunday.Stay with Wheels24 for the 2015 F1 season – fresh reports every week.