Playing elder sister tougher than facing top-ranked players for Mirra Andreeva

Russian teenager Mirra Andreeva has beaten the world's best players to move up to world number seven but on Wednesday she beat a player who had got the better of her for years - her elder sister Erika.

The Andreeva sisters were drawn against each other at the Stuttgart Open but any hopes of a witnessing an absorbing sibling rivalry were put to bed when Erika, 20, was forced to retire with a knee injury while trailing 6-2 1-0.

Mirra had beaten the likes of world number one and two Aryna Sabalenka and Iga Swiatek en route to the Indian Wells title last month, but the 17-year-old said it was tougher to focus when her elder sister is on the other side of the net.

"For me, 75 per cent-80 per cent is about my mental preparation, because you're also not just focusing on yourself and you're not focusing on how to beat her, but you're also focusing (on her) - does she feel good? I don't know," Mirra told reporters.

"I wonder, how does she feel? What are we going to do after the match? How is it going to be? All those thoughts.

"Me, I don't just focus on myself, but I also focus on kind of paying more attention to her. This makes the match more difficult for me... To really just focus on myself, it's almost impossible when I play against her."

The two had met once before in Wuhan last year where Erika - who is now 90 rungs below Mirra in the rankings - triumphed in straight sets.

Mirra said she knew Erika was struggling with her knee as they are sharing a room, but also revelled in beating her for the first time - even though the victory did not come under ideal circumstances.

"We played a couple of times on the practices when we were younger, and actually, until Wuhan last year, we never ever played an official match. So we were always