Catalyzes the condensation of the acetyl group of acetyl-CoA with oxaloacetate to form citrate. This enzyme is highly Re-face stereospecific with respect to the C-2 of oxaloacetate. acetyl-CoA + H2O + oxaloacetate = citrate + CoA + H(+) Can also use magnesium with lower efficiency. Inhibited by p-chloromercuribenzoate (pCMB), EDTA, Zn(2+) ions, and under aerobic conditions. Belongs to the alpha-IPM synthase/homocitrate synthase family.