The world number one, chasing an eighth Miami hardcourt crown, will face either third-seeded Simona Halep or fellow American Sloane Stephens for a place in the final.
Williams is the eighth player to win 700 WTA matches.
Martina Navratilova owns the most match wins, with 1,442.
Williams claimed her 16th straight victory at Miami, taking her record in the event to 71-7.
Germany's Lisicki had a set point chance in the first, but was unable to convert.
She was broken to send the set to a tiebreaker won by Williams.
Williams looked to be on her way when she broke Lisicki in the first game of the second set.
But the German responded, dominating the set before Williams -- who claimed her 19th Grand Slam title at the Australian Open -- regained her concentration and sealed the win in just over two hours.