The central Spanish government, which fiercely opposes the idea of an independence referendum, was quick to praise the vote.
Foreign Minister Jose Manuel Garcia-Margallo called the outcome "a good result for Catalonia, Spain and Europe, though not for Convergence and Union."
Deputy Prime Minister Soraya Saenz de Santamaria described the election as "a serious blow for Mas" but one that "put the priorities in order."
"Voters want governments focusing on the crisis and creating jobs," she added.
In all, the ruling party in Catalonia lost 12 seats, going down to 50 seats in the 135-seat regional legislature, with the Republican Left coming in second with 21 seats. Five other parties split the remainder, with most of those seats going to parties opposed to independence.
Mas did not immediately outline Monday how he will try to form a government. Republican Left leader Oriol Junqueras said voters had issued a "mandate to hold a referendum" but he ruled out forming a coalition with Convergence and Union.
Junqueras said his party would continue to demand that Mas' government change its austerity policies, calling for lower taxes for most and for banks and the rich to shoulder more costs. But he didn't rule out working with Mas on specific issues.
Jordi Matas, a political science professor at the University of Barcelona, said Mas might try to seek a limited deal with the Republican Left only on the referendum and other issues that falls short of a coalition.
While pro-referendum parties won a majority in the vote, Matas said the result of a hypothetical referendum is too hard to predict.
Mas' only other options for coalition partners are the center-right Popular Party or the center-left Socialist Party â¿¿ but he would have to drop his push for a secession referendum because both vigorously oppose such a vote.