Williams defeated Danka Kovinic 6-3, 6-3 at Arthur Ashe Stadium in Flushing Meadows, New York City - the site of Williams' first US Open victory in 1999, when she was 17 years old.
Earlier this month, Williams, now 40, announced her plans to retire from tennis, after a decade-long career in which she dominated and transformed the women's game, including 23 Grand Slam singles titles.
Serena Williams says she intends to retire from tennis after US Open
Williams has won six U.S. Open singles championships, the last in 2014. On paper, she is the overwhelming favorite on Monday night, with a 20-0 record in U.S. Open first-round matches — without dropping a set since 2001, according to the U.S. Open.
Serena Williams won her first match