Serena Williams earned bragging rights over Venus Williams as the 23-time grand slam champion dispatched her older sister in straight sets to reach the US Open last 16.

The most iconic sister act in sport, Serena and Venus were meeting for the 30th time – Friday's contest marking the earliest the pair have clashed at a slam since their first professional encounter at the 1998 Australian Open.

Venus beat her 16-year-old sister in straight sets that day in Melbourne but the seven-time major winner was no match for her younger sibling at Flushing Meadows, where Serena prevailed 6-1 6-2.

Serena capitalised on Venus' poor first-serve percentage to make it six successive slam victories against her 38-year-old sister, with the latter without a major win since the 2008 Wimbledon final.

Friday's high-profile match on Arthur Ashe Stadium in New York came almost a year to the day since former world number one Serena gave birth to her daughter Alexis Olympia.

And the 36-year-old – whose last major match against her sister was in the 2017 Australian Open final when she was pregnant – was a mother on a mission early, bringing up a double break-point opportunity in only the second game of the match after Venus sent a shot wide to highlight the contrasting start between the pair.

Venus managed to dig herself out of a 15-40 hole to hold serve against Serena, who called for the trainer after appearing to twist her ankle on the baseline.

Serena took a medical timeout and received treatment on her heavily strapped right ankle, but emerged seemingly pain-free as she finally converted a break for a 3-1 lead.

There was no stopping Serena from there, the 17th seed proving too strong and powerful in a first set wrapped up in half-an-hour.

A six-time US Open champion, Serena continued where she left off in the second set as broke in the very first game to put Venus well and truly on the back foot.

Serena's dominance was telling and, while Venus managed to get on the board in set two on her own racquet after spurning a break point, it was a relentless display from the younger Williams sister.

STATISTICAL BREAKDOWN
Serena Williams [17] bt Venus Williams [16] 6-1 6-2

WINNERS/UNFORCED ERRORS
Serena – 34/22
Venus – 14/18

ACES/DOUBLE FAULTS
Serena – 10/3
Venus – 1/0

BREAK POINTS WON
Serena – 4/10
Venus – 0/1

FIRST SERVE PERCENTAGE
Serena – 63
Venus – 67

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Serena – 88/37
Venus – 48/45

TOTAL POINTS
Serena – 69
Venus – 44