Romelu Lukaku has given Inter the 2-0 half-time lead with a penalty and pouncing on a lucky ricochet, but Lazio dominated possession.
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With Milan and Juventus losing on Saturday, the Nerazzurri knew a victory would put them in first place, but the Biancocelesti were coming off six consecutive Serie A victories and pushing for joint third place.
Arturo Vidal was the only absentee for the hosts, so Christian Eriksen started on his birthday. Luiz Felipe and Thomas Strakosha missed out for Lazio, with Stefan Radu pulling out in the warm-up, replaced by Wesley Hoedt.
To mark Chinese New Year, Inter players had their names written in Chinese characters on the back of their jerseys.
Eriksen set up two good opportunities for Marcelo Brozovic and Lautaro Martinez, but both were blocked by defensive interceptions, while Samir Handanovic came flying outside the area to clear from Joaquin Correa.
Romelu Lukaku knocked it on for Lautaro Martinez and Hoedt dived in with a mistimed sliding tackle, as he got some of the ball, but probably not enough. Lukaku sent Pepe Reina the wrong way to convert the spot-kick.
Milan Skriniar avoided a similar fate with a crucial tackle to stop Correa going clear, as Lazio continued to have more of the ball and Handanovic made a one-handed save on Ciro Immobile’s daisy-cutter.
However, it was Inter who were more direct on the counter-attack, despite being the home side, as Reina had to smother at Lautaro’s feet on another Eriksen assist and then smother a Lukaku snapshot.
VAR was involved again for the second Inter goal, which was initially disallowed for offside. Brozovic’s sliding tackle ricocheted off Manuel Lazzari’s shin and into the path of Lukaku to score. It was not an intentional pass. However, when Brozovic made the initial touch, Lukaku was level and therefore Lazzari’s contribution was irrelevant.
Inter 2-0 Lazio (Half-Time)
Lukaku pen 22, 45 (I)
Inter: Handanovic; Skriniar, De Vrij, Bastoni; Hakimi, Barella, Brozovic, Eriksen, Perisic; Lautaro Martinez, R Lukaku
Lazio: Reina; Patric, Acerbi, Hoedt; Lazzari, Milinkovic-Savic, Leiva, Luis Alberto, Marusic; Correa, Immobile