Udinese and Napoli missed the chance to move into the Champions League qualifying positions following a 2-2 draw in Udine on Sunday.
Lazio's earlier 1-0 defeat at Catania meant that if either side had won, they would have gone third but instead the draw leaves them both a point behind the Romans.
Udinese will be ruing a missed opportunity having led 2-0 through goals from Giampiero Pinzi and Antonio Di Natale.
But after Diego Fabbrini was sent off, Edinson Cavani snatched a point with a brace whilst also missing a penalty.
Udinese have now won only one of their last seven league games while Napoli's five-match winning run in Serie A came to an end.
And Udinese coach Francesco Guidolin, who was sent off as well for protesting against the penalty award, could not hide his disappointment.
"There's a lot of bitterness, I had to spend quite some time in the dressing room calming down the lads," he said.
"But I don't want to talk about the referee or incidents, we hoped we'd get back to winning ways in my 100th game in charge of Udinese but it went badly."
Napoli boss Walter Mazzarri saw things quite differently.
"We deserved to win, over the 90 minutes we played better," he said. "Even when it was 11 against 11 we played better than them."
The hosts took the lead on 28 minutes when Pinzi made a clever diagonal run to arrive free in the box to tap home Fabbrini's right wing cross.
Di Natale then tapped home at the back post on 52 minutes after Pinzi's header had come back off the bar.
Fabbrini was harshly sent off for a second booking on the hour mark after an innocuous clash with Hugo Campagnaro.
Maurizio Domizzi gave away a penalty for a handball but Cavani's strike, hit hard and straight, came back off goalkeeper Samir Handanovic's knee.
The visitors were on a roll, though, and Cavani left Handanovic rooted to the spot with a curling free-kick from 20 yards on 81 minutes.
And the Uruguay forward bagged a second with a fierce left foot drive that went in off the near post five minutes from time.
Lazio had much the better of their clash in Sicily but succumbed to Nicola Legrottaglie's goal from a corner 10 minutes from time.
The Romans had created good chances for Stefano Mauri and Miroslav Klose but couldn't find the finish they needed, losing for the second game in a row.
Lazio stay third ahead of Napoli's trip to Udinese later on Sunday.
"We did well and created four chances but we have to improve and become more clinical and determined in the final phase," said Lazio coach Edy Reja.
But Catania moved level on points with Inter Milan and Roma and are now securely in the battle for a European finish.
Inter failed to win for the eighth time in nine league games, as their hopes of playing in Europe next season took another hit following their 0-0 draw at home to Atalanta.
It was also the sixth time in those nine games they had failed to score and a fifth home league game in a row without a win.
With just 10 games left, they are six points behind the European qualification positions and seven off a Champions League finish.
Inter only had themselves to blame after Diego Milito missed a first half penalty.
Gianpaolo Bellini was harshly adjudged to have brought down Giampaolo Pazzini in the box but Andrea Consigli plunged low to his left to keep out Milito's weak 24th-minute spot-kick.
That was as close as Inter got to scoring in an uninspiring game in which their problems in front of goal were all too plain to see.
Coach Claudio Ranieri seemed at a loss to explain how they could turn around their fortunes.
"We want to do well but we're not managing it. This year everything's going badly but I can't reproach the lads for anything," he said.