Mirra Andeeva hailed her sister Erika as the person who "showed me the way" after the elder sibling was forced to retire from their Porsche Grand Prix match. The two Russian stars had only played against each other once before Wednesday's clash in Stuttgart.

Mirra won the first set 6-2 and led 1-0 in the second before Erika had to stop playing. Her right knee was heavily bandaged before stepping foot onto the court and she likely feared worsening the issue, had she continued to fight what appeared to be a losing battle.

Advancing to the last 16 where she will face Ekaterina Alexandrova, Mirra spoke glowingly about her sister during an on-court interview: "We shared the same room so of course I knew what she has been going through.

"Honestly I have weird emotions, I should be a little bit happy that I won the match but still I am super sad that it ended like this. But I am sure that she is going to take her time and she is going to recover and come back as strong as she can.

"If she didn't start playing tennis before me I don't think I would play this well, this fast. She started playing some tournaments that she didn't have to and showed me the way, because of her I am high [in the rankings] now.

"It [was] easier for me to start to play bigger tournaments right away. If she wasn't there I am not sure I would be playing this tournament this year."

Mirra, 17, has had a fairly comfortable run to the last 16. Her first-round opponent Marta Kostyuk pulled out of their tie due to an injury she suffered on international duty at the Billie Jean King Cup.

The Ukrainian's withdrawal ensured that both of last year's finalists in Germany were absent, with defending champion Elena Rybakina pulling out before the tournament along with Zheng Qinwen and Ons Jabeur.

Andreeva will be hopeful of taking advantage of such big-name absences and continuing her strong start to the WTA campaign, claiming a 14th win from 15 matches this season on Wednesday against her sister.

The winner of this year's event in Stuttgart receives a free Porsche car as a prize and Andreeva revealed she has already been window shopping - even though she doesn't have a license.

“The view on the centre court is super nice. I already thought about which cars I would like to get,” she said earlier this week. “But we're not there yet. I'm just looking around. I still don't have my driver's license. Yeah, we're going to see. We're going to decide if I get to the final.”