By Alan Baldwin

RIO DE JANEIRO (Reuters) - Ryan Murphy completed a backstroke double and extended a U.S. winning streak on Thursday, adding the Olympic men's 200 meters gold to the 100 title he won earlier in the week.

The U.S. men have now won the event for six successive Olympics dating back to Atlanta in 1996.

"That one was very painful but I wanted it bad. The 100m backstroke comes more naturally for me," said Murphy. "The 200 back is an event I really have to dig deep for.

"This medal means a little more to me."

World champion Mitch Larkin, who had been tipped to become only the second Australian to win a backstroke gold and the first since 1960, had to settle for the silver medal.

Russian Evgeny Rylov clinched bronze.

"There's a lot of pressure. Unfortunately Ryan came over the top of me," said Larkin, who arrived in Brazil as a big hope capable of going home with two golds but who finished fourth in the 100m backstroke.

"This week was a massive learning experience.

"For me I guess the silver lining is the learning curve that comes with it. That is just handling the pressure. This is my first major international meet that I've gone in where everyone is watching."

Murphy, a 21-year-old first time Olympian, trailed Larkin over the first 50 meters but took the lead after the turn and stayed ahead to touch out in one minute, 53.62 seconds -- the fastest time of the year.

He will be heavily fancied to take his third medal of the Games in Saturday's medley relay, having set an Olympic record in winning the 100 backstroke.

Larkin finished in 1:53.96, beating world junior champion Rylov (1:53.97) by the closest of margins.

Tyler Clary, the gold medalist at London 2012, was unable to defend his title after failing to be selected at the U.S. trials.

(Reporting by Alan Baldwin, editing by Greg Stutchbury)