Williams faced Vera Zvonareva, whose slide in the tennis world the previous two years could largely be attributed to injury and illness. The crafty Zvonareva is a former world No. 2 -- and took on Williams on a much grander stage, the Wimbledon final, in 2010.
Zvonareva was still a heavy underdog Thursday and playing without pressure, built up three set points on the Williams serve at 5-3 in the first set. Trouble for the world No. 1.
But just as Maria Sharapova and Rafael Nadal stepped up when their backs were against the wall Wednesday, so did Williams.
She erased all three of the set points to hold.
It was the start of a 10-game run that propelled the 18-time grand slam winner to a 7-5 6-0 win on the first day of sweltering conditions -- temperatures reached almost 36 degrees Celsius in Melbourne -- at the year's opening major.
"Things really clicked," Williams told reporters. "I had no other option but for things to click. I just had to start playing better."
Williams dropped just eight points in the second set, an ominous sign for her third-round foe, Elina Svitolina.
Williams' older sister, Venus, also progressed to the third round by crushing fellow American Lauren Davis 6-2 6-3.
Serena said she continues to draw inspiration from Venus, who was diagnosed with the autoimmune disease, Sjogren's Syndrome, in 2011.
"She's like, 'Yeah, if I win it'll be great. If not, I'm not going to worry about it,'" Serena said. "I think that's a great attitude because it takes a lot of pressure off of you.
"She's done so much in her career. She doesn't have to win another match. The same thing for me. As long as we can kind of look at it that way, then we both will do really well."
Another marquee second-round clash saw two-time Australian Open champion Victoria Azarenka tangle with U.S. Open finalist Caroline Wozniacki. After a close first set, the rejuvenated -- and healthy -- Azarenka won 6-4 6-2 and celebrated by dancing on court.
She's on course to tangle with Williams in the quarterfinals.
Last year's Wimbledon champion, Petra Kvitova, beat Germany's Mona Barthel 6-2 6-4. Kvitova is one of the contenders at Melbourne Park this year, having triumphed in Sydney last week.
The 2013 Australian Open finalist, Dominika Cibulkova, is flying under the radar thus far -- which she probably doesn't mind.
And after getting past the tricky Kirsten Flipkens in the first round, Cibulkova crushed unpredictable Bulgarian Tsvetana Pironkova 6-2 6-0.
Another lucky escape
Sharapova saved match points in defeating qualifier Alexandra Panova, but it's an uncommon feat. Saving match points two matches in a row is almost unheard, yet veteran Feliciano Lopez has done it.
The Spaniard fended off three match points against American Denis Kudla, prior to saving one more Thursday in the third set versus Frenchman Adrian Mannarino.
Lopez, the 12th seed, eventually advanced when Mannarino retired with heat exhaustion while leading 6-4 6-4 6-7 (3) 0-4.
"I feel very lucky," Lopez told the Australian Open's website. "I think those two matches I won, I shouldn't (have) won, at least not the one today. I was very lucky."
There was no such drama for top-seed Novak Djokovic.
Djokovic needed less than an hour and a half to see off young Russian Andrey Kuznetsov -- who upset grand slam finalist David Ferrer at Wimbledon last year -- 6-0 6-1 6-4, but defending champion Stan Wawrinka had to work somewhat harder against Romanian qualifier Marius Copil. Wawrinka prevailed 7-6 (4) 7-6 (4) 6-3.
Despite the loss, Copil can take heart from the fact he hit the fastest serve of the tournament at 242 kilometers per hour.
In a week filled with mostly positive results for the Australians, favorite Lleyton Hewitt -- in his record 19th straight tournament appearance -- blew a two-set lead to fellow 33-year-old Benjamin Becker of Germany. Becker, previously 0-6 in fifth sets, came through 2-6 1-6 6-3 6-4 6-2.
U.S. Open finalist Kei Nishikori admitted to feeling slightly dizzy due to the conditions but still eliminated another big server, Ivan Dodig of Croatia.
Dodig failed to serve out the fourth set and Nishikori ran out a 4-6 7-5 6-2 7-6 (0) winner.
"Hot out there," said Nishikori. "A lot of sun. It wasn't easy. Especially third and fourth set I was a little bit dizzy and tired. But, you know, it's going to be like this in Australia, so I think I was ready for it. Hopefully I won't play (in) this condition again."
For Nishikori, the weather forecast looks promising.
The forecast high for the next two days is 27 degrees Celsius prior to the highs falling to the low 20s.