From the edge or the crease, Michalek deflected Matt Carle's shot past Nikolai Khabibulin.
Chicago rookie Jonathan Toews scored on his first shot in his first NHL game to give the Blackhawks a 1-0 lead at 13:43 in the first period.
After Toews was sent off for a hooking penalty in the second period, Michalek scored his first power-play goal, at the 10:28 mark.
Khabibulin made 30 saves. San Jose's Evgeni Nabokov blocked 16 shots.
Toews, the Blackhawks top draft pick and third overall in 2006, connected on his sixth shift. The 19-year-old forward had missed Chicago's first two games with a broken right index finger, suffered in a Sept. 19 preseason contest.
Toews centered a line with wingers Tuomo Ruutu and rookie Patrick Kane, the first-overall pick in the 2007 NHL Entry Draft.
Toews took a pass at the San Jose blue line, barreled past Sharks defenseman Matt Carle and beat Nabokov high on the glove side from the right circle for the opening goal.
Khabibulin stopped San Jose's Joe Pavelski with a glove save on a short-handed breakaway at 8:30 of the second.
While Toews was serving his second hooking penalty of the game, Michalek tied it 1-all at 10:28 of the second. Michalek fired a shot between Khabibulin's legs from the low edge of the right circle after working a give-and-go with Patrick Marleau.
San Jose's first goal came on its 21st shot.
Chicago killed a double-minor penalty to Brent Seabrook early in the third.
Notes: Toews was whistled for his NHL first penalty, for hooking, late in the first period. ... Blackhawks RW Martin Havlat missed his second game because of a right shoulder injury and is out indefinitely. Chicago D Andrei Zyuzin missed his third game because of a groin injury. ... San Jose D Douglas Murray and C Patrick Rissmiller were healthy scratches for the first time this season. Four Sharks sat out with injuries — D Brad Norton (back), D Alex Semenov (back) C Tomas Pilhal (shoulder) and RW Devin Setoguchi (ankle).