Serena, who in her first-round match was five points from defeat against world No.60 Bernarda Pera, rallied from a set down and then a 4-2 deciding set deficit to defeat her sibling in an entertaining two hour and 19 minute encounter.

"I've lost a few tight sets lately, so I was telling myself I really wanted to win this one and try to focus on those last two games," she said.

"I'm super relaxed. Having no crowd sort of makes things more relaxing. I've practised in louder places than this court.

"It was a very high quality match. There was a lot of long points, running me around and then at one point it was just big serves and so I thought that was really interesting as we both started serving really well and returning well."

Serena won three games in a row to lead 5-4 in the decider and served out the match, claiming victory on her first match point.

The American will next face either countrywoman Shelby Rogers or rising Canadian star Leylah Annie Fernandez.

The suspension of tennis caused by the COVID-19 pandemic meant that until this week, Serena had not competed on the tour since February.

As a result, the American said rather than focussing on winning the Top Seed Open, she wants to make sure she gets into top form for the August 31-September 13 US Open.

"I'm just here to play another match just to get match tough for New York," said Serena, who has failed to add to her haul of 23 grand slam titles since January 2017.

"I've done absolutely nothing but train and practise and so I am really low on the matches and so this is really helping."

Jil Teichmann is also through to the quarter-finals after overcoming Yulia Putintseva in straight sets.

The Swiss eased through 6-2 6-2 in just under an hour-and-a-half and will play Cici Bellis who defeated Jessica Pegula 6-3 6-2.

Australian Associated Press