Marco Delvecchio and Vincenzo Montella each scored twice in the first half as Roma dealt Lazio their first defeat of the season to move into second place and confirm their own title ambitions.
"It's hard to explain a defeat like this, especially since the match was virtually over after 10 minutes," Lazio's Swedish coach, Sven Goran Eriksson, said.
Lazio remain on 21 points, two more than Roma and Parma are a further point adrift. Parma, confirming their return to form after a miserable start to the season, came from behind to beat bottom-placed Cagliari 3-1, while nine-man Torino held on to win 1-0 on a snow-covered pitch in Verona.
Ronaldo scored to lead Internazionale in their rout of Lecce, which included goals by Ivan Zamorano, Vladimir Jugovic, Javier Zanetti, Grigorios Georgatos and Alvaro Recoba.
Ronaldo, however, limped off the pitch during the second half with a sprained knee and ankle to add to Inter's injury troubles. The Milan club are already missing the Italy striker Christian Vieri with a foot injury.
In Spain, Real Madrid discovered that life is likely to continue on much the same lines after the departure of John Toshack as they were held to a 1-1 draw at home by Real Sociedad yesterday.
Seeking their first victory at home in the league since August, Real Madrid took the lead through Savio Bortolini 11 minutes into the second half but gifted a soft equaliser 13 minutes from time to Jose Antonio Pikabeo.
The sending-off of Jose Mari Gutierrez shortly afterwards effectively put an end to hopes of a winning start under Toshack's replacement as coach, Vicente del Bosque.
With the leaders, Rayo Vallecano, losing 3-1 at Numancia, Celta Vigo took over at the top as they beat Valladolid.
In France, the Brazilian Sonny Anderson converted a late penalty to give Lyon a 1-0 home win over Lens and keep them at the top of the French First Division. Anderson, the league's leading scorer, took his tally to 12 with his fourth goal in three matches.
Lyon have 31 points from 16 matches, two more than second-placed Auxerre, who won away for only the second time when they scored a surprise 1-0 victory over Marseilles.Reuse content