Inter defeat Genoa in Serie A opener
Japan international Yuto Nagatomo headed in from point-blank range in the 75th minute following a deflected cross from Jonathan and Argentina striker Rodrigo Palacio doubled the lead in added time after an excellent through ball from Fredy Guarin.
Neither team had an attempt on target at the San Siro until a header from Inter substitute Mauro Icardi was blocked by goalkeeper Mattia Perin in the 53rd.
But Inter was in full control by the end and Icardi hit the crossbar with a header in the 82nd while Andrea Ranocchia had a header tipped wide by Perin a minute later.
While it didn't come easily, the result was significant for an Inter squad that finished ninth and had 16 losses last season, its worst effort in 65 years.
''It's a good start but we're only at the beginning. We need to improve a lot of things but we're on the right road,'' Inter midfielder Ricardo Alvarez said.
Mazzarri, who managed Napoli the past four seasons, was hired immediately after Andrea Stramaccioni was let go by Inter at the end of last season.
Later, striker Gonzalo Higuain makes his Serie A debut as last season's runner-up Napoli opens against Bologna. Also, Lazio hosts Udinese with one end of its stadium closed as punishment for fan racism in last weekend's Super Cup.
On Saturday, Juventus began its bid for a third straight title with a 1-0 win at Sampdoria while AC Milan was stunned 2-1 by newly promoted Hellas Verona, which got two goals from Luca Toni.