Juventus's 2-0 away win at Livorno on Sunday sent Antonio Conte's men top of the pile for the first time this season with a two-point lead on Rudy Garcia's men.
Roma were widely expected to retake the lead but despite dominating the Sardinians at the Olympic Stadium the Giallorossi were left counting the cost for failing to get the ball past impressive Cagliari 'keeper Vlada Avramov.
To add to their woes, Garcia was sent to the stands with 18 minutes remaining after an altercation on the touchlines.
"This was an unexpected result. People often say if you can't win, the next best thing is not to lose. But we had a really good game, created a lot of chances and in the end showed that the best player on the park was their goalkeeper."
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What will go down as a stirring performance from Cagliari was also one that, says coach Diego Lopez, was to help soothe the pain brought by flash floods which swept through the island last week, killing 16 people.
"This week we suffered a catastrophe... The lads ran their legs into the ground tonight to help pay tribute to the people of Sardinia," said Lopez.
It was the first time this season Cagliari had kept a clean sheet, and Lopez added: "It's difficult to come to a ground such as this. I asked a lot of my defence tonight and I'm really happy because it's our first game this season without conceding a goal.