MELBOURNE, Australia — It was a time-warp Saturday for Serena Williams at the Australian Open as she crushed the suspense out of a third-round match in Rod Laver Arena against an intimidated opponent and fielded questions in the interview room about her extracurricular activities: fashion, studies and even that old standard, acting.

“I actually have a gig in a week or two,” she said. “I’m excited about it.”

Despite the familiar setting and subjects, much has changed for Williams as she embarks on her latest tennis season down under. She is now 30: the same age as one of her measuring sticks, Roger Federer, although she was not prepared to concede the years at first.

“I’ll be 26 instead,” she said in an interview later.

After her health scares and on-court disappointments in 2011, she no longer holds any Grand Slam singles titles. The last of her 13 titles came at Wimbledon in 2010. She clearly recommitted herself to the chase in the offseason, however. She arrived in Australia trimmer and fitter than usual after changing her diet in the offseason, partly to show solidarity for her older sister Venus Williams, who is battling the anti-immune disorder Sjogren’s syndrome and did not make the journey here.

“Venus changed her diet, and we live together, so I can’t bring bad food into the house,” Serena said. “I kind of joined the train instead of being off it. I’ve always been a pretty clean eater, but I’ve just never, like, been this clean. I’m eating more veggies now, and I’m just eating more, not necessarily raw, but more raw. Not eating a lot of meat. I’ve never been a huge meat eater, but I don’t even like meat so much anymore.”

The benefits might have been more noticeable on court here if she had not torn ligaments in her left ankle during her warm-up tournament in Brisbane. That forced her to race the clock in an attempt to get healthy for the Open, which she first played as a 16-year-old and has won five times, including the past two times she played it, in 2009 and 2010.

“I felt like if I hadn’t got that injury, then I would have been able to do more things and felt even better, so I’m kind of trying to work my way into this event,” she said. “So I’ll see next event, see how it goes.”

She remains very much a part of this one, however. She has yet to drop a set in three matches, getting her best test in the opening round against the counterpunching of the Austrian Tamira Paszek. There have been some shaky patches of play: some gaffes at the net, some backhand errors linked perhaps to the fact that her backhand requires her to push off her left leg. But she has moved surprisingly well so far and served patiently and effectively on the few critical points she has faced, continuing to generate the intimidating pace that has helped make her a champion. (She had the fastest serve of the tournament so far at 118 miles per hour.)

To sum up, the overall impression has been positive, and her opponent on Saturday, the 32-year-old Hungarian Greta Arn, who had never played her before, was certainly complimentary. She set the tone even before the match began by calling Williams “the player of the century” and saying it was a privilege to play her. She soon relayed the same message to Williams directly, meeting her at the net after losing, 6-1, 6-1, in just 59 minutes.

“I’m a big fan of her, she’s the real No. 1, and so I think she’s going to win the tournament,” Arn said. “She does things differently than other players. The way how she walks into the court, the way she hits the ball, the way how she does everything is different, and that’s what I like.”

The opposition should soon get stronger and less conciliatory, however. In the fourth round today, Williams will face Ekaterina Makarova, the unseeded Russian left-hander who upset a compatriot, seventh-seeded Vera Zvonareva, 7-6 (7), 6-1, in the third round.

If Williams beats Makarova, she will play in the quarterfinals against the winner of the match between fourth-seeded Maria Sharapova and No. 14 Sabine Lisicki. Sharapova, playing with renewed ferocity, has dropped just five games in three matches. Petra Kvitova, the No. 2 seed who won Wimbledon last year, is also in the same half of the draw and advanced Saturday with ease after Maria Kirilenko retired with a leg injury. Kvitova was leading, 6-0, 1-0.

“It’s only going to get tougher and tougher for Serena each round, but I think she’s ready for it, and I think she’s going to do well,” said Aleksander Bajin, her longtime hitting partner.

Williams is on anti-inflammatory medication for her ankle and said she remained on blood-thinning medication in the wake of the pulmonary embolisms she experienced last February, when she was rushed to an emergency room in Los Angeles.

“I’m totally OK now,” she said. “I feel like I can totally go on, I’m still checking with my doctors, still take medicine for it. I still go in, and they check my lungs and it’s a lifelong process. This is a long trip for me, but when I go back, that is the first thing I have to do, get back situated with that whole kind of thing. But yeah, I just appreciate every moment. You never know what tomorrow brings, if tomorrow comes.”

Williams speaks from experience: the murder in 2003 of her half-sister Yetunde Price and the death last month after an extended illness of Keven J. Davis, her family’s longtime legal adviser and confidant.

“Life just comes at you so fast,” Williams said. “Just in February, he was visiting me in the hospital and hanging out in L.A. and having a blast and how quickly things go. When you lose someone that close to you, it’s definitely hard, but in this situation it was easier for him to go, because he was in a lot of pain. But it wasn’t easy for us, but you know, his sins are all forgiven now so we can take comfort from that.”

Williams said she struggled to find a grand design.

“I never believe things happen for a reason,” she said. “Like there’s a reason my sister was murdered? I never believed in that, but I do believe that unforeseen things happen at unforeseen times, which is actually a scripture from Ecclesiastes.”