Reigning gold medallist Natalie Cook ended up with an aching head, a sore shoulder and a place in the Olympic beach volleyball quarter-finals after one of the most emotional matches of her career.

Cook and partner Nicole Sanderson beat fellow Australians Kerri Pottharst and Summer Lochowicz 21-15 21-16 in the round of 16.

But the victory was tinged with sadness for Cook who had teamed with Pottharst to win bronze in Atlanta in 1996 and the gold medal in Sydney four years ago.

"If it was fair, we'd all have gold medals," Cook said.

The match carried added significance for Pottharst whose comeback from to the sport is over at the age of 39.

Pottharst had returned to action this year following a relationship break up and teamed with Lochowicz in a successful late bid to qualify for the Athens Games.

After breaking down in tears as she started telling journalists of a decision that seemed inevitable, Pottharst composed herself and praised both her partner and opponents.

"I'm getting to old to be running around out there with all these young ones," Pottharst said.

"It's time I went home and got a life back again....go and do my garden and feed my cat."

Pottharst said she hoped to turn to coaching and to get involved in the corporate side of her sport.

Brought to you by AAP © 2024 AAP