Opposition parties in Chad have condemned a planned two-day visit by France's far-right leader Marine Le Pen to the former French colony on Tuesday 21 March.
Fillon, a one-time front-runner who has fallen back over by a scandal surrounding the employment of his wife as a parliamentary assistant, has been put under formal investigation, a first for a French presidential candidate.
A quick poll of TV viewers taken after the debate showed that in their eyes Macron was the most convincing candidate in the debate ahead of Jean-Luc Melenchon.
"Stop immigration, and I will not make any excuses for that", she said, stressing that France's security situation is "explosive" and measures need to be taken "to discourage immigration".
Le Pen, among the frontrunners in the French presidential election, travelled to Lebanon in February to get a sense of the Syrian crisis and is using the two-day visit to meet French troops stationed in Chad and outline her policies for Africa.
Le Pen said the burkini was a sign of the "rise of radical Islam in our country" and accused Macron of supporting it.
Political parties of the Chadian opposition, civil society movements and representatives of the Chadian diaspora are protesting against the French politician's visit to the capital N'Djamena, describing her as a xenophobe. He really needed to do well in this debate, trying to revive this campaign after weeks of legal woes and allegations.
She and Mr Macron are leading opinion polls in an election that comes as France struggles with high unemployment and a sluggish economy.
Early on, the candidates clashed over the teaching of French in schools - the first subject in the TF1 debate.
"I completely disagree with Emmanuel Macron who praised the German chancellor when he was in Berlin for (refugee) policies that turned out to be bad policies and which are now criticised by her own allies in Germany", Fillon said in a slap at his centrist rival.
Fillon, a former prime minister, concluded the debate by saying: "I have some flaws".
The candidates then discussed the issue of immigration, a key theme in this year's presidential election. Polls now show Le Pen and Macron looking likely to make it through to the second, final round, but the race remains open and impossible to predict.
Le Pen, known for her tough stance on migration, spoke in favor of closing the nation's borders, pointing out that France must handle the issue itself, as "we can't count on Greece to deal with the flow of migrants".