|Looking up: Motta helped keep Inter on course for the treble [AFP]
Treble-chasing Inter Milan powered back to the Serie A summit with a 2-0 win at Lazio which was bizarrely celebrated by both sets of fans.
Even though the defeat means Lazio are still not safe from relegation with two matches to go, their supporters were glad bitter city rivals Roma had slipped back to second spot.
Inter, two points clear of Roma, scored with headers from Walter Samuel and Thiago Motta either side of the break.
Sampdoria and Palermo remained locked in battle for fourth place and the final European Champions League qualifying spot after both recorded Serie A wins – while Juventus had to make do with a Europa League place.
Sampdoria, who lead Palermo by two points, at times laboured to a 2-0 success at home to relegated Livorno while the Sicilians held on to a 2-1 victory at Siena.
Antonio Cassano scored the only goal of the game after just five minutes as he got beyond the defence and beat goalkeeper Alfonso De Lucia.
Cassano should have given Sampa breathing space six minutes before the break but somehow contrived to fire wide from a great position.
The frustratingly inconsistent Cassano was having one of his champagne days on the pitch and twice set up Giampaolo Pazzini but he couldn't finish.
However, six minutes from time Swiss full-back Reto Ziegler crashed home a free-kick to calm Sampa nerves.
Siena joined Livorno in Serie B next season after their relegation was confirmed by the defeat to Palermo.
Uruguayan forward Edison Cavani gave the visitors the lead on 24 minutes after converting a cross from Antonio Nocerino.
When Fabrizio Miccoli added the second just before the hour mark, the game seemed over but 10 minutes from time Emanuele Calaio headed home a cross from former Middlesbrough forward Massimo Maccarone to set up a tense finish.
In other games Napoli and Juventus both ensured themselves a place in the Europa League next season.
Napoli won 2-1 away to Chievo thanks to goals from Argentine pair German Dennis and Ezequiel Lavezzi, sandwiching a Pablo Granoche strike.
Juventus dropped to seventh, a point behind Napoli, but secured their spot with a 1-1 draw at Catania due to Genoa's 3-0 defeat at Bari.
Bologna boosted their survival hopes as they came back from a goal down to draw 1-1 at 10-man Atalanta.
Bologna need only one more point from their final two games to ensure survival while Atalanta will be relegated unless they win their last two matches and Bologna lose both of theirs.