Milan, who ended Inter's five-year reign as Italian champions by winning the scudetto in May, fought back through ex-Inter striker Zlatan Ibrahimovic and Kevin-Prince Boateng.
Inter dominated the first half with Dutch midfielder Wesley Sneijder, heavily linked in the media with a move to Manchester United or City, firing in the opener on 22 minutes with a free-kick after Gennaro Gattuso had escaped a red card.
Ibrahimovic equalised with a header against the run of the play in the 60th minute after being set up by Clarence Seedorf and nine minutes later Boateng scored the winner.
"A derby game is always a derby. We really faced difficulties with stamina in the first 30 minutes as players looked tired," Milan coach Massimiliano Allegri told a news conference after the season curtain-raiser.
"But in the second half, it has turned out to be much better. We did not give any more chances to Inter except Wesley Sneijder."
The defeat was an inauspicious start for new Inter coach Gian Piero Gasperini, who replaced Leonardo during the close season as the Brazilian became Paris Saint-Germain sports director having had short spells as both Milan and Inter boss.
"We played very well in the first half," Gasperini said in a bid to find some positives.
"As for the rumour of Sneijder leaving, we will talk about it next week after we go back Italy."
Gasperini's appointment disappointed many Inter fans given he was sacked by modest top flight side Genoa early last campaign and has no big club experience.
His penchant for three at the back, rare in European football nowadays, has also raised eyebrows but his side got off to a good start only to let Milan impose themselves like they did in the two derbies last season which practically swung their first Serie A title since 2004 their way.
Transfer movement over the break has been limited for both clubs but despite the familiarity, the match had the feel of a friendly given there are several weeks before the actual season begins.
The new league season starts on August 28 when Milan travel to Allegri's former club Cagliari and Inter, Italian Cup winners last term having won the treble the previous season under Jose Mourinho, host Lecce.
The games are under threat of a strike by the Italian players' association over a long-running disagreement with the league over a collective contract, with two strikes narrowly averted last season.
The Super Cup was played in the packed Bird's Nest Olympic Stadium in Beijing in front of over 70,000 under a deal between the league and Chinese authorities to host Italy's season curtain-raiser there four times over six years.
Lazio previously beat Inter at the Bird's Nest in 2009.
"I came from Sichuan province with a bunch of Milan fans to Beijing just to watch the Milan derby," 29-year-old Dai Wei, wearing a Milan shirt, told Reuters as he entered the stadium.
An Italian campai
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