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Maria Sharapova has made her Twitter debut at the Australian Open, and she's tweeting on THE trend of this year's tournament.

"Everyone got dressed in the same closet, wearing yellow on court at the aus open," she tweeted Tuesday. It was only her second posting and she already had more than 50,000 followers.

Yellow is hands down the color of choice among players — or rather, sponsors — at this year's Australian Open. Yellow sneakers, yellow shorts, yellow dresses, yellow visors.

For fans in the upper decks, it can be hard to tell who's who on certain courts.

Former No. 1 Caroline Wozniacki wore a white-and-pale yellow tennis dress designed as part of her Adidas line with Stella McCartney.

It was very similar to the white-and-pale yellow Nike dress on her opponent, German Sabine Lisicki. It didn't help that both wore visors over their blond ponytails. Wozniacki won and faces Donna Vekic of Croatia in the second round.

Some men were sporting yellow, too, including France's Gael Monfils whose fluorescent muscle T-shirt matched the tennis balls and was only slightly brighter than the yellow shirt of his 18th-seeded opponent Alexandr Dolgopolov.

"The colors are a joke," said 73rd-ranked Timea Babos of Hungary. "It's the same for everyone — yellow, grey and white."

She should know. Way out on Court 22, Babos played hard and lost to France's Kristina Mladenovic, 6-3, 4-6, 11-9 in a nearly three-hour battle against a player who looked like her mirror image.

The two wore identical yellow tank dresses with white and gray trim — which provided some comic relief, Babos said, smiling through tears after her loss.

"Having the same outfit was hilarious," she said, adding that it was the talk of the locker room. "Everyone was joking about it. They said, 'It doesn't matter, you look better.'"

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ADVICE FROM CHINA: French Open champion Li Na had some advice for her close friend and compatriot Wu Di the night before he made history by becoming the first Chinese man to play in the singles draw of a Grand Slam tournament in the Open era.

"Last night before I go to bed I get a text message from her," said Wu, who is from Li's hometown of Wuhan and frequently practices with her. "She told me, 'Don't be nervous. Don't think about tennis. Just go to bed. Your answer will be tomorrow, not tonight. So, don't think about anything else.'"

Li speaks from experience. She became the first Asian player to reach a Grand Slam final at the 2011 Australian Open and then the first Asian winner of a Grand Slam at Roland Garros.

Wu, ranked 186th in the world, lost his first-round match Tuesday at Melbourne Park against Croatia's Ivan Dodig, 7-5, 4-6, 6-3, 6-3. But he the 21-year-old who mostly plays on the lower-level Challenger and Futures circuits fought hard.

The speedy Wu kept points lively as he ran down Dodig's heavy forehands and drop shots and forced the Croatian player into countless errors. When he broke Dodig's serve to go up 5-4 in the second set, his red-clad Chinese supporters in the stands broke into a raucous cheer: "Jia you, Wu Di," which roughly translates as "Let's go, Wu Di."

Frenchman David Moreau, Wu's coach for the past eight months, said the Chinese player has the game to compete in more Grand Slams but he needs to be more decisive and aggressive on court.

"Of course, he needs to improve his serve. He's a short guy, but he's been improving a lot already. And now it's going to be about moving forward into the court," he said.

Wu is aiming to qualify for the French Open men's draw next, but isn't so optimistic about his chances.

"Of course, I want to participate two Grand Slams in a row, but red clay is not my strongest surface," he said.

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ANDY'S NEW LOOK: Andy Murray has had to explain that his chest is not more muscular, it just looks that way because he's wearing a tighter shirt this year.

Since Murray started working with coach Ivan Lendl, he has certainly bulked up.

"Most of the weight that I put on is in my legs. But the T-shirt I'm wearing is tighter," said the stolid Scotsman, when told he seemed to be filling out his shirt better this year.

In his mumbling monotone, the 25-year-old added: "It's not that I'm any bigger in my upper body. It's just because of the tightness of the T-shirt, maybe it appears that way."

Third-ranked Murray advanced to the second round at the Australian Open on Tuesday, beating Robin Haase of the Netherlands in straight sets, 6-3, 6-1, 6-3.

It was his first Grand Slam match since his career-changing win at the U.S. Open in September, which came shortly after he won the men's gold medal at the London Olympics.

He attributes much of his success to Lendl. During an on-court interview he joked that Lendl is relaxed "in front of the cameras, yeah," but, "behind closed doors he works me very hard."

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A TRUE FAN: It was a first-round match so important for Caroline Wozniacki that it kept her golf star boyfriend, Rory McIlroy, awake at night.

The former No. 1-ranked Wozniacki came back from 3-0 down in the final set to win the last six games of the match against big-hitting Lisicki 2-6, 6-3, 6-3.

McIlroy got up at 3 a.m. to watch from Abu Dhabi, where he's preparing to play in this weekend's Abu Dhabi HSBC Championships. He was coming off a busy day himself after the announcement of his lucrative multi-year contract with Nike.

Of course, the multimillion dollar golf contract became a topic of conversation.

"It wasn't really a big surprise to me. I kind of knew," she said to laughter in her post-match press conference. "I felt bad for him because I think he went to bed at midnight their time and woke up at 3 and watched me and then back to sleep for a couple of hours."

"That's a true fan," she added.

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Associated Press writer Justin Bergman contributed to this report.