Innocent Emeghara struck a goal in each half as Siena moved off the bottom of Serie A with a 3-0 win over Lazio that simultaneously derailed the Roman club's increasingly dim title hopes.
Emeghara opened the scoring after only six minutes with a thumping header from Matteo Rubin's cross.
Alessandro Rosina doubled Siena's lead with a neat flick at the near post after another superb Rubin delivery.
Lazio improved after the break but Siena completed the scoring just after the hour when Emeghara raced clear and lifted the ball over Federico Marchetti.
With Internazionale having lost at Fiorentina on Sunday, Lazio were looking to create a gap between themselves and the other sides chasing Champions League football next season - and trim the seven-point margin separating themselves from second-placed Napoli.
But Lazio never looked comfortable against a Siena side desperate to move off the bottom of Serie A and towards safety.
Rosina was always a threat and he played a part in Siena’s opener after just six minutes. Dispossessing Michael Ciana, Rosina switched the play wide to Rubin, whose pinpoint cross from the left was met by Emeghara’s bullet header, which left Federico Marchetti helpless
That provided Siena with the injection of confidence they needed and before long they were two goals to the good. Rubin was again the provider, delivering a perfect cross from the left after Emeghara had released him with a neat back heel. Rosina darted ahead of his marker to deftly flick the ball beyond Marchetti at the near post.
Lazio’s best player was Antonio Candreva, but his dipping effort from distance was the closest Lazio came in a disappointing half for them.
Lazio improved after the break but had no cutting edge in attack and it didn’t take long for Siena to put the result beyond doubt. A deflected ball was touched on by substitute Francesco Valiani into the path of Emeghara, who raced away from Lazio captain Giuseppe Biava and dinked the ball over the advancing Marchetti.
Lazio coach Vladimir Petković threw on Ederson and Louis Saha in search for a way back, but the closest Lazio came was a free header for Ederson that was too close to Gianluca Pegola.
Siena were the superior side throughout and are now only four points from safety, while Lazio are left to rue a missed opportunity in their quest for Champions League football.