Chancellor Angela Merkel made the more convincing case to lead Germany for the next four years in Sunday's television debate against her election rival, Martin Schulz, according to viewers.

Forty-nine percent of viewers surveyed by German broadcaster ARD viewed Merkel as the more credible over the course of the debate, compared to just 29 percent who favored Social Democrat (SPD) candidate Schulz.

Read more: Merkel, Schulz debate as it happened

More than half of those surveyed (55 percent) said the chancellor also outperformed her rival, compared to just 35 percent who thought Schulz came out on top.

Merkel reportedly scored particularly high marks when it came to credibility, grasp of the issues and likability.

It comes after the two candidates jostled over 90 minutes on issues ranging from migration, to pensions, to Dieselgate.

Migration

Migration turned out to be the first and central issue of the debate, with Merkel remaining stern on her decision to open Germany's borders to hundreds of thousands of migrants in 2015, saying it was the "absolutely correct" thing to do.

While Schulz said he ultimately agreed with the chancellor's decision, he rebuked her over her handling of the crisis and accused her of failing to coordinate a better European response. "The inclusion of our European neighbors would have been better," Social Democrat (SPD) Schulz said, adding that earlier EU policy would have seen countries such as Poland and Hungary take more responsibility to helping settle refugees.

That forced Merkel to shoot back, saying that Hungarian Prime Minister Viktor Orban made clear from the outset that he was not willing to cooperate. "We had a very dramatic situation... There are times in the life of a chancellor when she has to decide," said the chancellor.

Read more: Could migration derail Merkel re-election express?

The two candidates also differed on what a future migration policy for Germany should look like. Schulz called for a pan-European law on immigration, financed through Brussels, while Merkel said she favored a skills-based policy that favored migrants with the skills and qualifications Germany requires.

Turkey

Berlin's increasingly strained ties with Ankara also took center stage during Sunday's televised debate, with Merkel announcing "it is clear that Turkey should not become a member of the European Union."

Merkel's statement on Turkey came just minutes after Schulz said he would move to formally halt Turkey's EU membership talks were he elected chancellor.

Merkel initially stopped short of endorsing formalling ending Turkey's EU accession talks because they were de facto already non-existent.  

She added that she didn't "see (Turkey) ever joining and I had never believed that it would happen."

Instead of formalling ending EU membership talks, Merkel said she would would look at imposing "real restrictions on economic contact" including through the European Investment Bank, EU aid, World Bank and by blocking talks on expanding Turkey's customs union agreement with the EU, a move that could hit billions of euros in potential Turkish exports to the bloc.   

Read more: Two more Germans detained in Turkey for political reasons

Trump and North Korea

As the candidates turned to North Korea and its latest nuclear missile test, Schulz said that US President Donald Trump's "unpredictability" made him the wrong person to deal with the rogue regime.

Merkel used this as an opportunity to hone her credentials as a global stateswoman, saying she had discussed the threat from Pyongyang with French President Emmanuel Macron earlier in the day, and that she planned to hold talks with Trump, as well as leaders from Russia, China, Japan and South Korea.

Read more: North Korea threat: Will Europe help South Korea, Japan militarily?

While she stressed that she disagreed with Trump on many issues, Merkel said the North Korean crisis was not something that could be solved with the US, adding that "one must say in the clearest terms that for us, there can only be a peaceful diplomatic solution."

Social justice

While the two candidates found relatively little to disagree on concerning foreign policy, Schulz played to his image as a champion of social justice.

Germany, he said, is a "clearly prosperous country," but many parts of society  - such as single parents, pensioners and the long-term unemployed - remain closed off from those benefits.

Read more: German issues in a nutshell: Hartz IV

Merkel defended her employment record, pointing out that in her 12 years as chancellor, the number of unemployed persons had halved from 5 million to 2.5 million.

The chancellor also rebuked claims from Schulz that the party wanted to raise the retirement age to 70. Merkel said "with absolute certainty" that would not happen under her watch. That prompted praise from her Social Democratic rival, who said he appreciated her "very clear position."

Dieselgate

There was little discrepancy between the two candidates when it came to the aftermath of the Dieselgate scandal, with both leaders supporting the continued use of diesel and opposing any ban on diesel-powered cars.

Merkel said the emissions scandal left her "appalled" and "extremely angry," but she said it was imperative to protect Germany's 800,000 car industry jobs. 

While Schulz has also said the industry should be protected, the SPD candidate accused the chancellor of opposing consumer class action lawsuits against carmakers. Merkel shot back, saying she supported a test case for declaratory action "in principle" but the proposal brought forward by SPD Justice Minister Heiko Maas was too bureaucratic. 

Read more: Dieselgate: the cozy ties between Germany's car industry and Berlin exposed

"We can agree that I will call the Minister of Justice tomorrow and ask him to provide a reworked version as soon possible."

That prompted Maas to respond over Twitter, saying: "Mrs Merkel could have called me any time. She has my number. Instead she blocked the MFK (legal test case) without providing any counterargument."

Former chancellor undermining Russia sanctions

Both candidates rebuked former Chancellor Gerhard Schröder after they were asked in a quick-fire round what they made of his new role as board member at Russian state oil giant Rosneft. 

Merkel naturally took a much harsher position against the man she defeated in the 2005 federal election, accusing him of undermining EU sanctions imposed on Russia. 

Schulz said he had advised Schröder against taking up the position on the Rosneft board, but maintained that the former SPD chancellor had done a great service for Germany, highlighting his decision to keep the country out of the Iraq war. 

While he wasn't pleased with the former chancellor's new role, Schulz stressed that this was a "federal election about the future of Germany, not the future of Gerhard Schröder."