Updated

By Julian Linden

NEW YORK (Reuters) - Roger Federer has agreed to hire Paul Annacone as his new coach after the pair hit it off during a one-month trial.

Federer said Annacone would join forces with Swiss Davis Cup captain Severin Luthi in coaching him.

American Annacone, best known as the former coach of Pete Sampras and Tim Henman, joined Federer's camp earlier this month and the pair enjoyed instant success when the Swiss won the Cincinnati Masters.

Federer said Annacone had agreed to work with him on a part-time basis during the U.S. Open, starting on Monday, and would be part of his regular team once he finished his current job with the British Lawn Tennis Association (LTA) in November.

"Obviously he has had stuff to do for the LTA here and he will have things to do obviously after the U.S. Open, which I'm cool about."

Federer has experimented with several different coaches over the years whenever he felt his game needed improvement.

He won the Australian Open in January but was knocked out in the quarter-finals at the French Open and Wimbledon and slipped to third place in the world rankings.

He moved back to second place after winning in Cincinnati last week and the 29-year-old believes the inclusion of Annacone could be the key to getting back on top.

"It's just nice to hear a fresh, different voice for a change," Federer said.

"I just think the dynamics work really well with Severin, and Paul and me coming into the conversation just makes it really interesting. I can go with a very clear mindset into the matches."

Federer has won the U.S. Open five times, from 2004 to 2008, the same number as Sampras and Jimmy Connors. He lost last year's final to towering Argentine Juan Martin Del Potro.

(Editing by Clare Fallon)