The 26-year-old world number eight beat her Belarusian opponent, now ranked 52nd in the world, 6-4, 2-6, 6-2 on the Manolo Santana court at La Caja Mágica.

Azarenka spurned two break points at 1-1 in the deciding set and was unable to recover.

Stephens will face the winner of tomorrow’s match between China's Zheng Saisai and France’s Alizé Cornet.

Also through is second seed Petra Kvitová of Czech Republic after she defeated France's Kristina Mladenovic 6-3, 7-6.

The two-time Wimbledon champion is seeking to defend her title in the Spanish capital.

Among today’s other winners at the Women's Tennis Association Premier Mandatory event were seventh seed Kiki Bertens of the Netherlands and 12th-ranked Anastasija Sevastova of Latvia, who will face each other next.

Bertens overcame Latvia’s Jelena Ostapenko 6-4, 6-3, while Sevastova beat Romania’s Mihaela Buzărnescu 6-3, 6-4.

In the men's Association of Tennis Professionals World Tour Masters 1000 event, Croatia's Marin Čilić survived a scare against Slovakia's Martin Kližan to win 6-4, 2-6, 7-6 and progress to the second round.

The ninth seed saved four match points before eventually claiming victory.

One seeded player who did suffer elimination today was 14th-ranked Georgian Nikoloz Basilashvili following a 7-6, 3-6, 4-6 loss at the hands of the US's Francis Tiafoe.

There were no such problems for 11th-ranked Russian Karen Khachanov, who defeated Spain's Jaume Munar 6-4, 6-7, 6-3.

The Madrid Open, established in 2002, changed status from hard court to clay in 2009.

Competition in both the men's and women's events is due to continue tomorrow.