Top seed and defending champion Alexander Zverev will play his older brother Mischa in the last 16 of the ATP Citi Open, while Andy Murray continued his comeback in Washington.

After a combined 539 main-draw matches between the German brothers, Alexander and Mischa Zverev will finally go head-to-head at tour-level.

Alexander, 21, won the second set of his rain-postponed clash with Malek Jaziri 6-2 6-1 on Wednesday, while 30-year-old Mischa saw off wildcard Tim Smyczek 6-2 7-6 (8-6) midweek.

"I don't know him much because it's the first time we're playing," joked Alexander, who previously faced Mischa in qualifiers. "It's definitely not just another match, I think, for both of us... It's going to be very, very interesting for our family."

"It's a special day because not a lot of families can say that two brothers played against each other on such a high level... Obviously we both want to win. We won't give each other anything."

Mischa added: "I think it's going to be an interesting day."

Former world number one and three-time grand slam champion Murray also progressed to the round of 16 after outlasting fellow Brit and fourth seed Kyle Edmund in DC, where rain wreaked havoc again.

Murray – back on the hard-court circuit for the first time in 17 months – claimed a gruelling 7-6 (7-4) 1-6 6-4 win over Edmund to earn a showdown with Marius Copil, who stunned 14th seed Jeremy Chardy 6-4 6-4.

Belgian third seed David Goffin made it through after prevailing 6-2 1-6 7-6 (7-5) against Pierre-Hugues Herbert, Australian Open semi-finalist and eighth seed Hyeon Chung rallied to beat Marcos Baghdatis 6-7 (2-7) 6-4 6-3, and Kei Nishikori was too good for Donald Young 6-3 6-4.

French sixth seed Lucas Pouille was leading 6-7 (2-7) 6-4 3-0 when compatriot Vincent Millot retired, while there were also three-set victories for fellow seeds Denis Shapovalov and Stefanos Tsitsipas as Frances Tiafoe advanced in two.

The likes of Alex de Minaur and Andrey Rublev will return on Thursday to complete their matches.