Top seed Roger Federer moved into the quarter-finals of the US Open on Monday as opponent Mardy Fish quit before their match due to health reasons. The American had suffered with an accelerated heartbeat earlier this year, but underwent a medical procedure to repair the problem in May. Federer is bidding for his sixth title at the Open and has reached his 38th Grand Slam quarter-final. he led Fish 87-1 in their series with his only loss coming in 2008.