Williams won the Wimbledon singles and doubles titles in 2008
Third seed Venus Williams moved through to the quarter-finals of the Zurich Open with a determined 6-3 6-4 victory over Alona Bondarenko of Ukraine.
The 28-year-old needed to save a total of four break points in the match, one in the first set and three in the next.
"I played OK and when the points became important I was winning those, especially on my serve," she said.
Italian Flavia Pennetta set up a clash with top seed Jelena Jankovic after thrashing Nadia Petrova 6-1 6-1.
Williams, who will play Francesca Schiavone in the next round after the Italian beat Maria Kirilenko of Russia 6-3 7-5, admitted she needed to improve her sharpness as the tournament progresses.
"I was trying to put more into coming in (to the net) on different kinds of shots. I'll be looking to improve my level with every round," she said.
Meanwhile, Swedish qualifier Sofia Arvidsson overcame a wretched start to defeat Sybille Bammer of Austria 0-6 7-5 6-4.