venus williams 0-6 , 6-1 , 7-5 , key biscayne on tuesday and set up a semi-final clash with germany 's ninth seed andrea petkovic .
petkovic booked her place in the last four after a 6-4 , 6-2 win over 14th seeded czech karolina pliskova .
williams utterly dominated the first set , crushing the spaniard 6-0 in less than half an hour but her opponent was able to regroup and battle back in impressive style .