Three-times champion Venus Williams was almost the victim of a huge shock before finally beating unseeded teenager Alla Kudryavtseva 2-6 6-3 7-5.
Williams was singles champion in 2000, 2001 and 2005
Williams failed to win any of her first three service games and soon found herself a set and 2-0 down.
But she finally got into the match and turned things round to force a decider.
Kudryavtseva, 19, took a 3-1 lead in the final set but Williams fought back again and decisively broke in the 11th game before serving out for victory.
Williams was at a loss to explain her error-strewn start to the match.
"My balls were just flying out and I didn't have any answers. That bothered me. Usually I can figure it out and change my game but I was like 'what am i doing wrong?'" said the former champion.
It's great to be back as the defending champion here
"I just had to take something off the ball, try to add a little more spin and just go for consistency. I just took a step back and then took a couple of steps forward.
"I haven't played a match in two weeks. Hopefully, I've made my mistakes in the first round and hitting balls in pressure situations will help me in the coming rounds."
Amelie Mauresmo began the defence of her Wimbledon title with a solid win against Jamea Jackson on Centre Court.
The Frenchwoman has struggled for form this year but found something approaching her best against world number 158 Jackson, winning 6-1 6-3.
"It's great to be back as the defending champion here," said the fourth seed.
Sharapova's shoulder continues to give her problems
"I'm enjoying it. Maybe it's a little extra tension before you walk on the court but then during the match, it really feels good."
Second seed Maria Sharapova opened her campaign with a less than convincing 6-1 7-5 win over the impressive Yung-Jan Chan from Taipei.
The world number two looked comfortable early on, breaking the 17-year-old three times to take the first set in 32 minutes.
Sharapova had a tougher test in the second set and although she claimed a 4-2 lead, Chan broke straight back as the Russian looked edgy but she dug in and broke again to claim victory.
The 2004 champion is suffering from a long-term shoulder injury, but said: "The doctors have given me the green light to keep playing, and it's in my hands to manage the pain.
"Sometimes I don't have as much confidence in my arm as I do in other matches, but it's more of a strength issue than anything."
Fifth seed Svetlana Kuznetsova was a set and 4-2 down to Julia Vakulenko in the last match on Court One before fighting back to win 4-6 6-4 6-3.
However 11th seed Nadia Petrova wasted little time in her late-night match against unseeded American Vadia King, playing in only her second Wimbledon.
Petrova, a quarter-finalist on her last appearance two years ago, needed just 45 minutes to earn a 6-0 6-1 victory.