Lazio confirmed their victory in the 90+1′ following a Sergej Milinkovic-Savic header.
Following a foul on Manuel Lazzari by Matteo Darmian, Luis Alberto stepped up to take the consequential free-kick.
Up 2-1, the Spaniard could have played it short or backwards to try and time waste. However, he decided to whip in a cross towards the Inter six-yard box.
Milinkovic-Savic, who stepped in between Milan Skriniar and Stefan de Vrij, met the ball and put a header into the top right corner passed Samir Handanovic to give Lazio a 3-1 lead.