MADRID — Less than a week before Spain heads to the polls, Prime Minister Pedro Sánchez emerged mostly unscathed from a heated four-way debate.

In Monday night's televised debate, Sánchez's main political rivals managed to land a few punches on Catalonia and the economy but did little to damage to the prime minister's electoral prospects.

Sánchez's Socialists are polling in first place ahead of Sunday's election and are projected to win 129 seats, according to a poll of polls for El País published Monday. But while Sánchez appears on track for a major victory, the result is likely to force him to seek allies in parliament to back his reelection as prime minister.

The main opposition Popular Party, led by Pablo Casado, is polling in second place at 78 seats, followed by the liberal party Ciudadanos at 46 and the far-left Podemos and its allies on 35 seats. The far-right Vox — which was barred from participating in Monday's debate — is projected to win 30 seats.

An estimated 42 percent of voters are still undecided, however, and party leaders seized on the chance to convince them in Monday's debate. 

The incumbent Sánchez portrayed himself as the reasonable option among radical rivals in a bid to appeal to moderate voters across the political spectrum. He also went out of his way to address women, young climate change activists and rural voters, and highlighted his government's accomplishments, such as a 22 percent rise in the minimum wage.

“We can choose a country with more social justice or more inequality, with cleaner governance or more corruption, with better coexistence or with the entrenchment of territorial confrontation,” Sánchez told the audience in his concluding remarks.

The prime minister also fended off criticism from other candidates that he has been too lenient with Catalonia's ruling separatists and warned against the danger of a potential governing alliance between Casado's conservative Popular Party, the liberal Ciudadanos — whose leader Albert Rivera also participated in Monday's debate — and the far-right Vox.

“They’re going to put Mr. Casado as prime minister, Mr. Rivera as a companion in some ministry and the far right at the wheel,” Sánchez said. “This is a very threatening reality we need to avoid ... I thought Trump wouldn’t win, and he won; I thought Brexit wouldn’t happen, and it happened.”

Journalists watch the debate at RTVE studios in Pozuelo de Alarcón, Madrid | Pablo Blazquez Dominguez/Getty Images

Casado, meanwhile, adopted a more sober tone than Rivera, with whom he is competing for right-wing votes. His main lines of attack against Sánchez focused on the economy, which he argued has worsened since the Socialist government took office last year, and Catalonia.

“Spain’s unity is at risk because of the Socialist government,” Casado told viewers, claiming Sánchez is negotiating Catalonia’s self-determination with the separatists — which the prime minister denies.

He also warned the Spanish welfare state is "at risk," saying jobs are "going out the window" under the Sánchez government.

Liberal leader Rivera opted for a more aggressive tone, hitting out at Sánchez's deals with Catalan pro-independence parties and the far-left Podemos, while castigating Casado's Popular Party for its history of corruption.

“You’ve got the word ‘pardon’ written on your forehead,” Rivera told Sánchez in his first-round comments, referring to the prime minister's refusal to rule out granting a pardon — if sentenced — to the 12 Catalan separatist leaders that are currently on trial before the country’s Supreme Court on charges related to the region's October 2017 declaration of independence.

Rivera accused Sánchez of coming to power with the help of those behind what he called a "coup d'état" in Catalonia, as Catalan pro-independence lawmakers were among those supporting the Socialist leader's no-confidence vote against his conservative predecessor Mariano Rajoy last year. He claimed that Sánchez would accept their support again to remain prime minister.

He also said that Sánchez was likely to form an alliance with Pablo Iglesias' Podemos, warning that this would lead to a steep increase in taxes: “If Mr. Iglesias becomes Deputy PM, hold on to your wallet.”

The Podemos leader, for his part, mostly avoided a confrontation with Sánchez and attempted to portray himself as a potential coalition partner that could pull the Socialist leader to the left.

Iglesias also took credit for some of the bills Sánchez has passed with the backing of Podemos — such as the rise in the minimum wage — and repeatedly pressed the Spanish prime minister on whether he would try to reach a coalition agreement with Ciudadanos, rather than with Podemos, after the ballot.

“The single-party governments are over,” Iglesias said. “Are you willing to reach a deal with Ciudadanos or not?”

Sánchez did not rule out any potential agreement with Podemos, Ciudadanos or the Catalan pro-independence parties. Ciudadanos’ Rivera, however, did dismiss the possibility of entering into a governing alliance with Sánchez.