In Rome, Lazio was still smarting from a 4-1 defeat at home to Atalanta and was beset by injury problems.
It lost two more players to injury during the first half and also conceded the opener in the 30th minute when Ivan Perisic cut in from the left and managed to get the ball to Lautaro Martínez who turned and fired into the bottom left corner.
Martínez has scored in all three of Inter’s matches this season.
However, Inter has been weak at the back in its opening two games, conceding five goals, and its defense let it down again as Sergej Milinković-Savić was able to head home Francesco Acerbi’s cross for the equalizer 10 minutes into the second half.
Atalanta offered up another attacking masterclass, taking its tally to 13 goals in three games.
It was the league’s top scoring team last season with 98 goals.
Luis Muriel gave Atalanta the perfect start after just seven minutes and, although Diego Godin equalized on his Cagliari debut, further goals from Alejandro “Papu” Gomez, Mario Pašalić and Duván Zapata put the home side 4-1 up at the break.
João Pedro reduced the deficit early in the second half but Sam Lammers sealed the match with his first goal for Atalanta with nine minutes remaining.
Rafael Leão scored twice as AC Milan beat newly promoted Spezia 3-0.
Theo Hernández netted the other goal with a superb solo run. All the goals came in the second half.
Elsewhere, Parma picked up its first points of the season with a 1-0 win over Hellas Verona.
Benevento beat Bologna 1-0.
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