Williams, the world's No. 1-ranked player and seeking a sixth Australian Open title, needed only 63 minutes to get by Vesna Dolonc 6-1, 6-2. Williams won more than 70 percent of the points on serve and saved the only break point she faced.
She won more than half the points (25-of-48) off Dolonc's serve and converted four of her seven break chances.
The win was the 60th for Williams in Melbourne, tying Margaret Court for most match victories at the Australian Open. Court, who won the Australian Open women's singles title 11 times (1960-73), is one of two players with more championships at the tournament than Williams.
Williams will be going for the outright match record in a third-round pairing against 31st-seeded Daniela Hantuchova, against whom Williams is 8-1 all-time. The only Hantuchova win in the series came in second round of the 2006 Australian Open.
Weather was again an issue in Melbourne, where temperatures topped 105 degrees Fahrenheit. The heat spell was predicted to last through Friday but break dramatically Saturday when highs in the upper 60s are forecast.
Fourth-seeded Li Na gained a spot in the third round with a 6-0, 7-6 (7-5) decision over Belinda Bencic. Li lost only 10 points total in the first set and overcame 23 second-set unforced errors to advance.
A pair of seeded players exited the women's draw Wednesday. Monica Niculescu battled past 15th-seeded Sabine Lisicki 2-6, 6-2, 6-2, dropping her serve just once over the second and third sets. Casey Dellacqua ousted 18th-seeded Kirsten Flipkens 6-3, 6-0 by winning 57 percent of the points and having six breaks when receiving serve.
Unseeded players with wins Wednesday included Alison Riske, Mona Barthel, Laura Davis and Zheng Jie.