(AP) — Serena Williams roared back after falling behind in the third set to beat Ana Ivanovic 2-6, 6-3, 7-5 on Friday night to reach the semifinals of the Bank of the West Classic. The top-seeded and top-ranked Williams dropped three consecutive games to fall behind 4-3 and then ripped seven straight points to right the ship in front of a sellout crowd at Stanford. Andrea Petkovic ended Venus Williams' run in the tournament, beating the former top-ranked player 6-1, 3-6, 7-5 in the quarterfinals. Following a shaky start, the 25th-ranked Venus Williams picked up her game in the second set and appeared poised to take over the match. Serena broke back and used a pair of aces to take a 40-0 lead before ending it when Ivanovic's return went just wide. Varvara Lepchenko took care of qualifier Sachia Vickery, 6-1, 6-0, to earn her 400th career win, which includes all levels.