Inter Milan crushed Parma 5-0 at the San Siro on Saturday to keep their slim Serie A title hopes alive while Lazio's championship challenge took a hit when they crashed 4-0 to a vibrant and adenturous Siena.
Fifth-placed Inter moved to within a point of Lazio, one place above them, having hit nine goals in their last two games. They have won seven of their last eight league matches.
"These numbers are pleasing, we're correcting a situation that was complicated," said Inter coach Claudio Ranieri, referring to Inter's disastrous start.
However, he stopped short of suggesting they could challenge for honours this season.
"I'm not saying anything, I've arrived here and I'm trying my best. In April or May we'll see what we've done. Ahead of us there are teams who are running and we'll need to fly to be able to catch them."
It was also the third time this season that Parma have been thrashed by one of the big teams, having previously lost 4-1 to both Juventus and AC Milan.
Diego Milito scored a brace for Inter while he also had a hand in goals by Thiago Motta and Giampaolo Pazzini before youngster Marco Faraoni scored his first goal in Serie A late on.
Milito darted across his marker to flick home Ricardo Alvarez's left-wing cross at the near post after 13 minutes.
His deflected shot then dropped to Thiago Motta 20 yards out five minutes later and the Brazilian-born international lashed home a low drive.
Maicon crossed from the right four minutes before the break and Milito headed home to kill the game.
Milito then slipped in Pazzini on 56 minutes to clip home before 20-year-old Faraoni put the icing on the cake with a stunning volley that dipped over goalkeeper Antonio Mirante on 79 minutes.
In Siena, Mattia Destro scored a brace for the hosts and Emanuele Calaio added two penalties while the visitors had goalkeeper Albano Bizzarri sent off at the end of the first half.
The victory moved Siena up to mid-table while Lazio could drop to seven points off the leaders if either AC Milan or Juventus win on Sunday.
Lazio coach Edy Reja felt so embarrassed by his team's performance that he apologised.
"We didn't turn up, that was the worst performance since I came to Lazio," he told Sky.
"I want to say sorry to the fans and I take full responsibility. That today wasn't the same team that played very differently for the first half of the season."
Siena coach Giuseppe Sannino suggested Lazio's players still thought they were on holiday.
"Maybe Lazio weren't yet ready after the (winter) break, I'm not saying they made things easy but almost," he said.
This match was over by the break after Siena ripped Lazio apart on the counter-attack.
Lazio fell behind when Destro surged forward from midfield and shot across Bizzarri on 11 minutes, although centre-back Giuseppe Biava was guilty of leaving a gaping hole for the forward to attack.
Siena were awarded a penalty when Franco Brienza went down after trying to squeeze through a Marius Stankevicius and Lionel Scaloni sandwich, with Calaio scoring from the spot on 35 minutes.
But on the stroke of half-time the game was effectively ended as Destro ran between Stankevicius and Senad Lulic, the pair letting him pass all too easily, perhaps wanting to avoid giving away another penalty.
Destro dinked the ball over Bizzarri, who appeared to clip him with his foot.
The ball hit the post and Destro jumped up to slot home the loose ball except that the referee, perhaps somewhat prematurely, had already blown his whistle to give a penalty.
Bizzarri was dismissed and Calaio sent his second penalty into the same spot as his first, with substitute goalkeeper Juan Pablo Carrizo's first task being to pick the ball out of the net.
Destro rounded off the scoring nine minutes from time when he headed home Cristiano Del Grosso's cross.