Williams won 6-3, 6-4 on Monday to move on to face Anastasia Pavlyuchenkova in her first major quarterfinal since missing nearly a year with a series of health problems.
The 16th-seeded Serb actually had more winners Monday. But Williams minimized her mistakes on a windy afternoon in Arthur Ashe Stadium, with 14 unforced errors to Ivanovic’s 29.
Ivanovic had eight double-faults in the blustery conditions.
The 28th-seeded Williams is a three-time U.S. Open champion.