Sisters Serena and Venus Williams marched into the quarter-finals of the Miami Open after straight-set wins at Key Biscayne.

World number one Serena beat 24th seeded Russian Svetlana Kuznetsova 6-2 6-3 producing 29 winners and 20 unforced errors.

Serena has now won 18 straight matches and she is looking to add to her seven titles in Miami with her third straight triumph after winning in 2013 and 2014.

Venus continued a winning streak of her own -- making it seven wins in seven against fellow former world number one Caroline Wozniacki with a 6-3 7-6(1) victory.

The win also made it seven wins in her last eight against top 10 opponents, highlighting Venus's return to form after her health problems.

Romanian third seed Simona Halep won through after beating Italy's Flavia Pennetta 6-3 7-5.

Djokovic powers through

In the men's draw, defending champion Novak Djokovic defeated Belgium's Steve Darcis 6-0 7-5 to power into the last-16 along with Japan's Kei Nishikori and Canada's Milos Raonic.

The Serbian world number one, who just like last year won at Indian Wells before heading to South Florida, will face Alexandr Dolgopolov, a 7-5 6-4 winner over Brazilian Thomaz Bellucci, in the fourth round.

Fourth-seed Nishikori had even less trouble as he crushed Serbia's Viktor Troicki 6-2 6-2 in 63 minutes.

Source: Reuters