Eighteen-year-old Raducanu started the match where she left off in New York City, quickly winning the first six points in her first match since winning the Grand Slam.

Yet the Belarusian managed to weather the early storm, and broke first to open a 3-1 lead before breaking again and winning the first set in 30 minutes.

Sasnovich then kept the pressure on her opponent to close out a straight-sets victory.

Defeat at the first hurdle in California marks a disappointing return to action for Britain's Raducanu.

The player she beat in the US Open final, 19-year-old Leylah Fernandez of Canada, was a straight-sets winner over Alizé Cornet.

Czech seventh seed Petra Kvitová moved into the third round for the seventh time in her career with a comprehensive 6-2, 6-2 win over Arantxa Rus of The Netherlands.

Kvitová burst into an initial 4-0 lead and claimed the first set in half an hour, but world number 68 Rus picked up her play as the second set started although could not find a breakthrough and was eventually swept aside.

The world number 11 will face Belarus' Victoria Azarenka in the next round in a clash between two Grand Slam champions.

Former world number one Sir Andy Murray dismissed Frenchman Adrian Mannarino 6-3, 6-2 in his first appearance at the tournament in four years.

The Briton is a two-time Olympic champion but has struggled with injuries in recent years.

American wildcard Jenson Brooksby has set up a tie with third seed and Olympic champion Alexander Zverev of Germany after downing Turkish qualifier Cem İlkel 7-6, 6-4.

Brooksby's compatriot Frances Tiafoe improved his poor record in California after beating France's Benoît Paire 6-4, 6-4.

The 23-year-old was previously 1-4 at this Association of Tennis Professionals Masters 1000 event but looked comfortable as he broke Paire's serve four times on his way to the round of 64.

An all-American battle awaits as Tiafoe will face 32^nd seed Sebastian Korda next.