* Serena makes successful but tearful start
* Federer, Djokovic, Wozniacki ease through
* Stosur highest seed to fall, Isner beats Mahut in no time
LONDON, June 21 (Reuters) - Wimbledon has come to expect fighting instincts and effortless power from Serena Williams but the raw tears she shed after beating Aravane Rezai on Tuesday betrayed just how much torment she has suffered since holding the trophy aloft last year.
Roger Federer, Novak Djokovic, Caroline Wozniacki, Maria Sharapova and Li Na made short work of their opponents and the John Isner against Nicolas Mahut re-match inevitably failed to live up to last year's epic so it was Williams who captivated the crowds in blustery conditions on Centre Court.
After crunching down an ace to earn a 6-3 3-6 6-1 win over tenacious Frenchwoman Rezai, defending champion Williams covered her face and wept before walking off to generous applause from a crowd delighted to see her back on the hallowed turf.
"I never dreamt I would be here right now," said the 29-year-old American, who only returned to action last week in Eastbourne after 49 weeks out with a foot injury and a pulmonary embolism that left her on her death bed.
"I just wanted to win just one match here seeing as I'm not playing doubles, it was just a really big win for me.
"It's been so hard and a disaster year for me, but I've been praying and I have my family here and I just love tennis," added 13-times grand slam champion, whose older sister Venus also won through on Monday after her own injury troubles.
Andy Roddick, another American who has become a favourite son in this leafy suburb of London courtesy of his three final defeats by Federer, also progressed to the second round by beating German qualifier Andreas Beck 6-4 7-6 6-3 on Court One.
His nemesis Federer battled the wind and the awkward serve of Kazakhstan's Mikhail Kukushkin to prevail 7-6 6-4 6-2 on Centre Court, his usual slew of breathtaking shots helping the fans forget the bracing chill.
"The first match at Wimbledon is never easy. I struggled to get enough returns in during the first set," said the Swiss third seed, who saw champion Rafa Nadal progress on Monday.
"It was tricky conditions, a lot of wind. It was really strange how the wind came in."
Serbian second seed Djokovic, whose 43-match winning run was ended by Federer in the French Open semi-finals, began his quest for a first Wimbledon title with a quickfire 6-4 6-1 6-1 demolition of Frenchman Jeremy Chardy.
Juan Martin del Potro, the 2009 U.S. Open champion, crushed Italy's Flavio Cipolla 6-1 6-4 6-3 and reliable Spaniard David Ferrer beat Benoit Paire 6-4 6-4 6-4 but fifth seed Robin Soderling and former winner Lleyton Hewitt laboured through.
As a stream of fans from across the world made plans to leave the South London venue late in the day, French hope Jo-Wilfried Tsonga livened them up with a typically energetic display to defeat Go Soeda of Japan in straight sets.
Isner met Mahut in a sequel to last year's freakish 11-hour battle of survival but this time the American shrugged off the Frenchman 7-6 6-2 7-6 in just over two hours to leave the day's focus squarely on Serena.
Almost a year after beating Vera Zvonareva to win her fourth singles title on the lush green lawns, Williams returned to her favourite stage having played just two competitive matches in the 11 months since due to her huge health scares.
With an alarm wailing in the stands and spots of rain falling from the cloudy skies, the first game lasted nine minutes in which time Williams was foot-faulted twice, made rudimentary errors and even had trouble with her hair band.
To make matters worse, Rezai came out swinging from the hip and looked in the mood to cause a shock.
Williams, who had never lost a grand slam first round match in the 43 she has contested, slipped 2-0 behind but soon found her swagger and reeled off the next five games.
Rezai hit back to level after breaking in the sixth game of the second set before Williams regained control and swept through the decider in 25 minutes.
Top seed Wozniacki had no trouble in disposing of Spain's Arantxa Parra Santonja 6-2 6-1, French Open champion Li Na powered past Alla Kudryavtseva and her Chinese compatriot Peng Shuai also went through.
Fifth seed Sharapova stormed past Russian compatriot Anna Chakvetadze 6-2 6-1 and the two surprise women's semi-finalists from last year eased into round two.
Czech left-hander Petra Kvitova beat America's Alexa Glatch 6-2 6-2 and Bulgaria's Tsvetana Pironkova followed with a 6-2 6-1 win over Italian Camila Giorgi.
Former world number one Jelena Jankovic crashed out to Spain's Maria Jose Martinez Sanchez and Australia's number 10 seed Samantha Stosur became the highest seeded casualty in either draw after losing to Hungarian Melinda Czink. (Additional reporting by Mark Meadows; Editing by Ed Osmond)