Senad Lulic and Keita Balde got the goals to put Lazio back into European contention. Cagliari missed a crucial penalty while they were trailing by a single goal and had captain Daniele Conti sent off late on.
Cagliari coach Diego Lopez played under Reja during the 68-year-old's brief time in Sardinia, and the two shared a warm embrace before kickoff. Danilo Avelar and Davide Astori were suspended for the hosts, as was Antonio Candreva for Lazio. Federico Marchetti lined up against his former club.
The home side fashioned the game's first chance after ten minutes. Andrea Cossu cut inside the Lazio box and forced Marchetti into a one handed punch to send the ball clear. Five minutes later, Miroslav Klose drilled a dangerous ball across the box for Vlada Avramov to run out and smother.
Lazio took the lead on 19 minutes thanks to some route one football. Klose, then Alvaro Gonzalez flicked on a goal kick for Lulic to run clear and lift the ball over Avramov into the top corner. It was the Bosnian's first league goal since September.
Gonzalez should have added a second on 27 minutes. Lulic turned provider for the Uruguayan to head his effort into the ground and wide at the far post.
Victor Ibarbo fashioned a chance out of nothing after half an hour. The Colombian lifted the ball over Giuseppe Biava and ran at goal, but with no-one in support, the forward had to go it alone and he shot straight at Marchetti.
Conti had picked up a yellow card for a foul on Keita and escaped a possible second booking, after his foul on Abdoulay Konko on the edge of the area went unseen.
Lazio continued to look dangerous after the break. Avramov ran out to punch clear a long Lucas Biglia cross, Daniele Dessena cut out Klose's intended pass for Lulic, then Keita ran into the box and curled a shot inches over the bar.
On the hour, a burst of pace took Klose past Dessena, but the German lost his footing and sent his effort into the side netting. Keita rescued a cross on the byline, only to see his shot bounce off Avramov's chest.
Cagliari were handed an opportunity to get themselves back on level terms from the penalty spot. Biglia was penalised for kicking Matias Vecino midway through the second half, but substitute Mauricio Pinilla sent his effort wide of a diving Marchetti. Lazio instantly punished their wasteful hosts by doubling their advantage. Klose weighted a perfect pass to release Keita, with the youngster burying a low shot past Avramov into the bottom corner.
Avramov used his body to block Keita, while Marchetti was on his toes to tip over a long range effort from Agim Ibraimi. Conti was walking a disciplinary tightrope and Cagliari lost their captain 13 minutes from the end. Conti caught Biglia in the face with a trailing arm right in front of the referee and was given his marching orders.
Keita wasted another chance in the closing stages. The Lazio man drew the Cagliari defence out of position as he ran across the box, only to send his shot into the stands.
Cagliari: Avramov, Dessena, Rossettini, Pisano, Del Fabro, Conti, Ekdal, (Sau 75) Cossu, (Ibraimi 46) Ibarbo, Vecino, Nene (Pinilla 57)
Sent off: Conti 77
Lazio: Marchetti, Konko, Biava, Novaretti, Radu, Gonzalez, (Onazi 81) Ledesma, Biglia, Keita, Klose, (Mauri 90) Lulic (Anderson 89)
Goals: Lulic 19, Keita 69