- Serena Williams continues winning run against Eleni Daniilidou in Cincinnati
- World No. 2 says her "super crazy" hair was a distraction during the match
- Serena's sister Venus also victorious against 12th seed Maria Kirilenko
- Andy Roddick loses to Jeremy Chardy in the men's draw after suffering a back injury
Not many opponents have come close to beating Serena Williams in recent months, but the tennis star had to overcome her own "super crazy" hair to win her first match since claiming double Olympic glory.
The world No. 4 continued her imperious recent run with a 6-3 6-4 win against Greek qualifier Eleni Daniilidou at the WTA Tour's Cincinnati Open for her 35th victory in 36 singles matches.
Williams has won singles and doubles Olympic gold at London 2012 and the Bank of West Classic since being crowned Wimbledon champion for a fifth time last month.
However, the second seed was left frustrated after making 44 unforced errors against Daniilidou on Tuesday as she began preparations for another tilt at her home U.S. Open later this month.
"That's shocking. It's unprofessional. Hopefully I clean up my act for my next match," the 30-year-old told the WTA Tour's website ahead of her last-16 clash with either Poland's Urszula Radwanska or Kazakh qualifier Yaroslava Shevdova -- who she beat in the last 16 at Wimbledon.
On her hairstyle, Williams remarked: "I need to calm it down. It's really big. It was a little windy, so it was getting in my face, and I put it in this '80s scrunchie I happened to have.
"The look isn't new. I've just let it go super natural and super crazy and not care. It's fun."
Williams has won 66 singles and doubles titles in her career, but the 14-time grand slam champion was a little unsure about where Cincinnati featured in her resume.
"I've won this tournament. I have. When it wasn't this big. But it counts," the American said before reconsidering. "I did win this tournament, didn't I?
"Maybe I didn't. I can't keep up. I don't think I did. Okay, whoops. Yeah, I didn't win this tournament. I thought I did. I really thought I did."
Williams' older sister Venus, her gold medal-winning doubles partner at London 2012, is also yet to win the hard-court tournament.
The former world No. 1 has struggled in recent years with injury and illness, having been diagnosed with Sjogren's Syndrome during last year's U.S. Open.
But the wild-card entrant battled past Russia's 12th seed Maria Kirilenko 6-3 6-7(5-7) 6-2 in her first-round match before discussing her ongoing health problems and her ambition to play in a fifth Olympic Games in 2016.
"I'm trying different things all the time," said the 32-year-old seven-time grand slam winner. "I keep working with my doctors.
"Nothing can prevent bad days, but the bad days aren't as bad as they used to be. Now I realize I have to hang in there if I'm not having the best day. My main goal is to be 100%, but it's not like it goes away.
"It's still in my body trying to fight against me, but I'm fighting against it as well ... I can't wait until Rio. I'm very excited about Rio. That will probably be my last one. By that time I'll be creeping up in age."
Samantha Stosur, who beat Serena Williams in last year's U.S. Open final to win her first grand slam title, survived a spirited fightback from Spain's Anabel Medina Garrigues to win 6-3 6-7(6-8) 6-4 in Cincinnati and also reach the last 16.
The third seed let match point slip in a second-set tie-break and fell 4-0 behind in the decider before rallying to win six games in a row.
"It was an interesting third set considering the whole match was really quite close," said the Australian. "There were no breaks in the second set, and then straight away I got myself in quite a hole quite quickly.
"I thought I could still regroup and close that gap just a little bit, and if you do that, you never know what can happen. I got on a roll and managed to squeeze it out."
In the men's tournament, 2003 U.S. Open champion Andy Roddick is out after injuring his back during a 7-6 (7-4) 6-3 defeat to French lucky loser Jeremy Chardy.
The former world No. 1 now faces a race against time to fit for the Flushing Meadows grand slam.
"I just had a little bit of a back issue the other day in practice," the 29-year-old told the ATP Tour's website.
"I was supposed to play yesterday and we had a late request to delay it. I felt fine early on, and then I had one lunge forehand and, we have all had it, your back kind of goes out or spasms a little bit. It got progressively worse."
Meanwhile, American 10th seed Mardy Fish began his campaign with a straight-sets win over Spaniard Feliciano Lopez, while his compatriot Sam Querrey set up a meeting with Britain's defending champion Andy Murray -- the Olympic singles gold medalist -- by beating Austria's Jurgen Melzer.