Venus returns with Eastbourne win
The five-times Wimbledon champion, playing her first match since January's Australian Open third round when she retired after one game also against Petkovic, looked completely at home on the slick grass courts.
The 30-year-old, who has suffered from abdominal and hip injuries, did take a couple of tumbles on the centre court and double-faulted twice in her opening service game in blustery conditions but looked delighted to be back.
"It was definitely an adventure today...the conditions, falling down on every point," a jovial Venus, whose sister Serena has also chosen Eastbourne to launch a comeback from injury after a long absence, said.
"I was extremely excited coming back with a win against a player who has been playing so well the last 12 months."
Eighth seed Petkovic took advantage of some early rust in the Williams game as the American struggled to control her forehand in the seaside conditions but, after leading 4-2, she was broken in the eighth game and the set slipped away.
Petkovic, one of the most improved players on the tour this year, hit back to level as the sun broke through on centre court but Williams, who turns 31 this week, raised her game when it mattered to claim victory.
"It was interesting when I drew her," Williams said of the draw which pitted her against her last opponent.
"It was a tough match for her. That was a little bad luck for her but a great opportunity for me - it felt fitting, I guess. It was just very ironic."
Venus has not played at Eastbourne since she came through the qualifying rounds in 1997 while Serena, the 13-times Grand Slam champion, made her only appearance a year later.
She will face either former world number one Ana Ivanovic or Julia Georges in the second round.
Serena, playing for the first time since winning last year's Wimbledon title, plays Tsvetana Pironkova in the first round on Tuesday.
The 29-year-old, who cut open her foot last July in Germany and then suffered blood clots on her lung this year, was handed a wild card for the pre-Wimbledon event.