U.S. Open champion Serena Williams 'having fun' after months of 'hell' Serena Williams win her fifth U.S. Open women's singles title 1 beat second seed Victoria Azarenka 7-5 6-7 6-1 in New York Williams had an operation to remove life-threatening blood clots from her lungs in 2011 The American has now won 17 grand slam singles titles (CNN) -- Two years after losing part of her lung during an operation to remove a life-threatening blood clot, newly-crowned U.S. Open champion Serena Williams insists playing tennis "is just fun now." 1's battle-weary opponents might not be having so much fun after Williams successfully defended the Flushing Meadows title she won in 2012 against the same opponent, beating second seed Victoria Azarenka 7-5 6-7 6-1 to secure her fifth singles championship in New York. It is a far cry from where the now 17-time grand slam singles champion was in July 2010 when she suffered a cut to her right foot and was later diagnosed with a pulmonary embolism which left her on her death bed. Read: Djokovic and Nadal to face off in men's final That 11 months of "hell" culminated in her descent to No. 175 in the world rankings in July 2011. Since then four grand slams have been won by Williams during a truly dominant 14-month spell. One more major triumph would see her sit level with legendary compatriots Martina Navratilova and Chris Evert in fourth position on the list of the most prolific female grand slam champions of all time. "It was the toughest thing I've been through in my life," the 31-year-old told CNN. One thing kept happening after another, blood clots in both of my lungs, I lost part of my lung, I had to retrain. I don't have two full lungs anymore. You go through this stage of thinking, 'Why does all of this keep happening.' It was really 11 months of hell. When I'm on that court and I'm facing opponents, I feel like I've faced so many tougher opponents that this is just fun now. Read: Tennis baby is a Twitter star Top award Rising star Wimbledon great Routed Riggs Iconic match Film double Wightman wonders Glittering prizes Star gathering Captain fantastic Happy 40th Williams' lung problems only became obvious when she was rushed into hospital after experiencing breathing difficulties en route to an Oscars party in March 2011. "Being in the emergency room and being in hospital for all of that time, not knowing if I would ever pick up a racket again, not even caring, just wanting to be healthy," recalled Williams. That was a tough time for me. She is indeed healthy again and operating at the peak of her powers at an age when many of her contemporaries are seemingly struggling to last the pace. Roger Federer has seen his vice-like grip on men's tennis loosen as he heads deeper into his 30s, while Wimbledon champion Marion Bartoli retired last month at the age of 28. Read: Why Federer's legacy is 'vulnerable' However, Williams maintains a childlike enthusiasm for sport, aided in no small way by the perspective she gained during her battle to regain her form and fitness. "I feel like just going for broke now," she said. I'm really focused on what I want to do, I'm just having a lot of fun out there. I'm like '31 is old,' but that doesn't seem like me. I don't act like it [her age] either so maybe that has something to do with it. Williams' muscular physique sets her apart from physically smaller opponents and she remains proud of how she managed to combine power with femininity. "It's OK to be strong and to be powerful and to be beautiful and to love who you are," she added. You can stand up to anyone and you can be proud of who you are, where you come from and be a positive awesome girl. CNN's Will Edmonds says Serena Williams can match Steffi Graf's record haul of 22 grand slam titles following her U.S. Open triumph. September 9, 2013 -- Updated 1224 GMT (2024 HKT) Two years after losing part of her lung during a blood clot operation, U.S. Open champion Serena Williams insists playing tennis "is just fun now."