American defeats Rezai to mark her return on big stage after a troublesome year while Wozniacki and Federer also go through first round.
Serena gets emotional after winning first game at Wimbledon
Serena Williams, the defending champion who described her recent struggles against life-threatening blood clots as like being on her death bed, broke down in tears yesterday on her Wimbledon return.
The four-time winner battled past Aravane Rezai of France 6-3, 3-6, 6-1 to reach the second round in what was only her third match in 11 months.
"I usually don't cry, I don't understand it. It's been so hard, I never dreamt I'd be here," said Williams, whose traumatic year started with a foot injury and then continued with emergency surgery to removed blood clots on her lungs.
"I just wanted to win at least one match here and since I'm not playing doubles it was a really big win for me. It's been so hard and has been a disaster year.
"To be able to come back at Wimbledon is pretty awesome, I didn't expect to play or do anything. I'm just excited. I've never cried with joy for anything. I kept thinking, 'This is Wimbledon'."
The 29-year-old Williams dropped the first two games of the match before racing through the next six games to take the first set.
Rezai, whose ranking has slumped to 61 from a career high 15 last year after suffering a controversial and public split from her father, dug deep to break in the sixth game of the second set on her way to levelling the match.
But Williams, desperate not to become only the second defending champion to lose in the first round, shrugged off stamina and timing problems to dominate the final set, claiming victory with her 13th ace.
She next tackles Romania's Simona Halep for a place in the last 32.
Caroline Wozniacki, the world No 1, got her bid for a first grand slam title off to a fine start with a 6-2 6-1 win over Spain's Arantxa Parra Santonja in swirling winds.
The 20-year-old Dane was never troubled by her 105th-ranked opponent. Wozniacki needed less than an hour to set up a second-round encounter with France's Virginie Razzano. After the win, she said: "I thought it was very difficult. It was my first match on grass, a real match. But then, you know, the wind was blowing everywhere," the Dane told a news conference.
"There was one point where I hit the ball and it almost didn't come over and then I hit the next one and it just flew."
Six-time Wimbledon champion Roger Federer cruised to a straight-sets victory over Mikhail Kukushkin from Kazakhstan on Centre Court.
The Swiss third seed saw off the grass-court rookie 7-6, 6-4, 6-2.
Federer conceded just two points on his own serve in the first set but Kukushkin, to his credit, took it to a tie-break.
Once Federer had moved into the lead there was no stopping him though, and he wrapped up victory with a mixture of serve-volley tennis and unstoppable groundstrokes.
Federer said: "Overall I was happy with my performance. It was windy out there and somewhat nerve-racking, because you don't get a chance to practise on Centre."
Novak Djokovic, the No 2 seed, defeated Jeremy Chardy 6-4, 6-1, 6-1. The Serbian, who has been in the form of his life this year, knows he has a great chance to win Wimbledon for the first time.
He said: "It's great to be back on Centre Court, the most famous in the world.
"It's my first grass court match of the season and I'm extremely happy with how I played.
Roger [Federer] and Rafa [Nadal]have been so successful on grass, and they deserve to be favourites here, but I'm one of the players waiting behind for his chance."
Andy Roddick maintained his record of never having lost a first-round match at Wimbledon with a 6-4, 7-6 (6), 6-3 win over Andreas Beck, the German qualifier.