Inter defeat offers hope for Milan and Roma
The leaders, who held a nine-point advantage in mid-February before winning just one of six games, could see their lead cut to a point if AC Milan beat visiting Chievo Verona on Sunday.
Third-placed AS Roma will also move just four points behind champions Inter, who have played 28 matches, with victory in their game in hand at lowly Livorno the same day.
"I think only Inter can lose the scudetto but if they do we want to be right there," Roma coach Claudio Ranieri, whose side won the last of their three titles in 2001, told a news conference on Saturday.
"Tomorrow is a crucial day, it could be the start of a new championship for us."
Inter's dip in form, which comes before Tuesday's Champions League last-16 second leg at Chelsea, has coincided with injury and suspension problems while coach Jose Mourinho has been banned from the dugout for the last three games.
Inter, who will look to protect a 2-1 lead at Chelsea's Stamford Bridge, have looked weary as they seek a fifth straight scudetto but Milan boss Leonardo does not expect a spectacular collapse.
"Inter's defeat won't be decisive, there are too many matches left but it's great to be so close and in a battle to make the championship even more exciting," the Brazilian said.
Inter's loss has helped re-invigorate an injury-hit Milan after Leonardo's side were dumped out of the Champions League following a 4-0 humbling at Manchester United on Wednesday.
"It's great to be in this position, especially after the game in Manchester," Leonardo added.
"We can move one point behind but then there are another 10 games and that's a lot. We've got to be consistent and continue to think game by game."