At an election rally in Thessaloniki last week, Antonis Samaras asked voters for a strong mandate to "change everything." As we went to press Sunday night, it looked like Greek voters had other ideas.

Mr. Samaras's center-right New Democracy has been sharing power with the center-left Pasok party in a caretaker government since November. Sunday's election makes New Democracy the largest single party in the Greek parliament. But early exit polls showed them with 17%-20% of the...