LONDON (AFP) - Venus and Serena Williams warmed up for the Wimbledon singles semi-finals by reaching the last four in the doubles on Wednesday. The sisters underlined their dominance in the women's game with a 6-2, 7-5 victory over Germany's Anna-Lena Groenefeld and America's Vania King. The fourth-seeded title holders face top seeds Cara Black of Zimbabwe and America's Liezel Huber in Thursday's semi-finals. The Williams sisters could find themselves facing off in Saturday's singles final then teaming up later in the day for the doubles final. In the singles, Venus faces world number one Dinara Safina, while Serena takes on another Russian in Elena Dementieva. Black and Huber beat Spanish 11th seeds Nuria Llagostera Vives and Maria Jose Martinez Sanchez 4-6, 6-3, 6-0. But another Spanish pairing did reach the semi-finals with Anabel Medina Garrigues and Virginia Ruano Pascual, the second seeds beating Russia's Alisa Kleybanova and Ekaterina Makarova 6-4, 7-5. They will face either Australian duo Samantha Stosur and Rennae Stubbs, the third seeds, or Germany's Kristina Barrois and Italy's Tathiana Garbin for a spot in the final. In the men's doubles quarter-finals, US pairing James Blake and Mardy Fish beat Sweden's Simon Aspelin and Australia's Paul Hanley 7-6 (7/5), 6-4, 7-6 (7/5). Blake and Fish face defending champions Daniel Nestor of Canada and Nenad Zimonjic of Serbia, the second seeds, for a place in the final. US twins Bob and Mike Bryan, the top seeds, have already qualified for the semi-finals. They will play either India's Mahesh Bhupathi and Bahamian Mark Knowles, the fourth seeds, or ninth seeds Wesley Moodie of South Africa and Belgium's Dick Norman.