Serena Williams battled nerves early but has commenced their US Open farewell campaign with a first-round victory over Danka Kovinic in front of a loud Arthur Ashe Stadium crowd on Monday.

The 22-time major champion, who will end her decorated tennis career after the Flushing Meadows tournament, triumphed in one hour and 39 minutes over the unseeded Montenegrin 6-3 6-3.

Williams will face a bigger test next on Wednesday against second seed Anett Kontaveit who eased past Jaqueline Cristian 6-3 6-0.

Given Williams' impending retirement, there was a sense of expectation but also trepidation inside the star-studded center court and the 40-year-old appeared nervous early on with two double faults in a row in the first game.

But after a topsy turvy first set that included five breaks of serve, Williams eventually got a stronghold of the contest.

Williams improved as the match wore on, hitting 23-18 winners, with Kovinic having 28-9 forced errors.

Kovinic won three games in a row after Williams led 2-0 early, but the American responded in the sixth game to break back to square it up and never looked back.

Williams was forced to save four break points in an epic service game before converting set point after back-to-back aces.

The six-time US Open champion broke Kovinic in the fifth game of the second set to assert her control on the contest, before clinching the match by breaking to love.

WINNERS/UNFORCED ERRORS
Kovinic – 18/25 
Williams – 23/25

ACES/DOUBLE FAULTS
Kovinic – 6/8 
Williams – 9/6

BREAK POINTS WON
Kovinic – 2/10
Williams – 5/11