The third-seeded Russian has twice stood by at the season-ending event in Los Angeles in case a player withdrew from the eight-player field at the last moment with injury.
Petrova was stretched all the way by her 93rd-ranked opponent and she had to recover from 1-3 in the final set before claiming victory.
Results (quarterfinals): Ana Ivanovic (Serbia and Montenegro) bt Tatiana Golovin (France) 7-5 6-3; Nadia Petrova (Russia) bt Sybille Bammer (Austria) 6-2 3-6 6-3.
MONFILS FACES GROSJEAN
LYON (France): French teenager Gael Monfils survived a poor start to tame compatriot Marc Gicquel 6-4 6-1 and reach the Lyon Grand Prix semifinals on Friday.
The 19-year-old Monfils will face another compatriot, Sebastien Grosjean, who overcame a strong challenge from Belgium’s Olivier Rochus to qualify 6-3 7-6.
Down 4-1 in the first set, Monfils, 36th in the ATP rankings, moved up a gear to snatch seven games in a row before wrapping up the second set.
Results (quarterfinals): Sebastien Grosjean (France) bt Olivier Rochus (Belgium) 6-3 7-6; Gael Monfils (France) bt Marc Gicquel (France) 6-4 6-1
NABANDIAN WINS
BASEL (Switzerland): Former champion David Nalbandian stamped his claim on a spot at the Masters Cup as he thrashed Paradorn Srichaphan 6-2, 6-2 Friday for a fourth straight quarterfinal success at the 829,000-euro Swiss Indoors.
Cypriot surprise packet Marcos Baghdatis, who underwent arm surgery earlier this year which salvaged his career, booked into his first career semifinal as he put out Argentine Jose Acasuso 6-7 (2/7), 7-6 (7/5), 6-3.
In later matches, fourth seed Fernando Gonzalez of Chile was aiming to end the run of British teenager Andy Murray while Dominik Hrbaty was facing another upstart from qualifying in Belgian Kristof Vliegen.
Nalbandian ripped through the first set in 22 minutes, then reached 3-0 in the second before Paradorn got a break back.
Results (quarterfinals): Marcos Baghdatis (CYP) bt Jose Acasuso (ARG) 6-7 (2/7), 7-6 (7/5), 6-3; David Nalbandian (ARG) bt Paradorn Srichaphan (THA) 6-2, 6-2.
HASSELT WTA RESULTS
HASSELT (Belgium): Results in the 170,000-dollar WTA event here on Friday:
Quarterfinals: Michaella Krajicek (NED) bt Nathalie Dechy (FRA ) 6-4, 6-3; Francesca Schiavone (ITA) bt Samantha Stosur (AUS) 6-3, 6-2.
ST. PETERSBURG OPEN:
St. Petersburg: Results from the St. Petersburg Open men’s singles quarterfinal matches on Friday.
Nicolas Kiefer (Germany) bt Nikolay Davydenko (Russia) 6-1 6-1; Robin Vik (Czech Republic) bt Mikhail Youzhny (Russia) 1-6 6-4 6-2; Thomas Johansson (Sweden) bt Greg Rusedski (Britain) 6-2 7-6(6); Fernando Verdasco (Spain) beat Kenneth Carlsen (Denmark) 6-4 6-2.—Agencies