Yahoo Sports reports: World number one Aryna Sabalenka stormed back from the cusp of defeat to beat Czech Nikola Bartunkova and reach the last four of the WTA event in Berlin on Friday. Bartunkova, the world number 62, stormed to take the first set and led 4-0 in the second as a visibly frustrated Sabalenka struggled on serve and could not pose any kind of danger with her return.