Williams picked up her first straight-set win in five matches since she returned this month after being away from the tour for nearly a year because of a series of health scares, including blood clots in her lungs.
Williams , seeded seventh, is trying to become the first woman since Steffi Graf in 1991-93 to win three consecutive titles at the All England Club.
Against Kirilenko, Williams saved the only break point she faced and put together a 32-9 edge in winners.
"The matches are getting better, my serve is getting better, so it's just getting the rhythm that I've been missing a little bit, and it's good," Williams said. "I just want to continue to serve better like I did today, and just hold on out there and just move, and just really more than anything enjoy myself and stay focused."
Wozniacki, still looking for her first Grand Slam title, swept Jarmila Gajdosova 6-3, 6-2 to make the fourth round for the third straight year.
Wimbledon is the only major championship in which the Dane has not reached at least the quarterfinals.
Sharapova, the only champion in the women's draw other than the Williams sisters, struggled with her game but still progressed relatively easily against Klara Zakopalova of the Czech Republic, winning 6-2, 6-3.
But, after falling behind 3-1 in the second set, Sharapova lifted her game to win five games in a row to finish off the 35th-ranked Czech player.
No. 18 Ana Ivanovic, a former top-ranked player and 2008 French Open champion, was knocked out by Petra Cetkovska, 6-2, 7-6 (0).
Information from The Associated Press was used in this report.