SANTIAGO, Chile (Reuters) - Socialist Michelle Bachelet led Chile's presidential elections on Sunday but had not won enough votes to avoid a potentially tight January run-off, probably against rightist candidate Sebastian Pinera. With more than half of votes counted, the government Electoral Service said Bachelet had 45.68 percent, trailed by rightist opposition candidate Pinera with 25.83 percent. Experts and officials said a run-off was almost certain. If elected Bachelet, a separated mother of three who was tortured and exiled during Chile's 17-year dictatorship, will become Chile's first woman president. Joaquin Lavin, another candidate from Chile's divided conservatives who have been...