Hulk's rocket of a strike on 53 minutes got Andre Villas-Boas's team off to a winning start in Group F, where they lie second on goal difference after Urawa Red Diamonds' 4-0 demolition of Western Sydney Wanderers.
In Group E, Kashima Antlers beat Ulsan Hyundai 2-0 and Brisbane Roar were held to a 0-0 home draw by Thailand's Muangthong United.
SIPG have splashed out 60 million euros on Brazilian midfielder Oscar, among other buys, in their bid for glory after they reached last year's quarter-finals under Sven-Goran Eriksson.
But a speculative effort from Hulk and another shot way over the bar from the Brazilian were the closest SIPG came in a tepid first half in front of a noisy Seoul crowd.
At the other end, Dejan Damjanovic had a chance to finish off a sweeping move from the hosts but the Montenegrin striker shot tamely at goalkeeper Yoo Hyun from close range.
Oscar's most significant moment of the first half came when he petulantly raised his hand to Lee Sang-Ho's throat and shoved the Seoul forward, earning a yellow card.
But the muscular Hulk brought the game to life with a moment of magic on 53 minutes, when he smashed a left-footed shot from well outside the box which swerved into the top corner.
- Reds run riot -
Six minutes later Damjanovic tumbled in the box, earning a soft penalty and a second yellow card for He Guan -- but the striker's scuffed spot-kick was easily saved by SIPG's Yan Junling.
Earlier, Japan's Urawa smashed four second-half goals past Western Sydney Wanderers to open their campaign with a thumping win.
Shinzo Koroki and Tadanari Lee struck within two minutes of each other before Tomoaki Makino and Rafael Silva also got on the scoresheet as the Group F visitors ran riot in Sydney.
The result gives Urawa an early boost in their campaign for a second Champions League crown, but dents the Wanderers' chances of emulating their fairytale title run of 2014, when the club was just two years old.
It was Lee who prised open the home defence on 56 minutes, when his perfectly placed through-ball released Koroki who finished smartly with the outside of his right boot.
Two minutes later and Urawa took a stranglehold on the game, when the Wanderers' defenders failed to clear and stood watching each other as Lee swept home the second goal.
Urawa capitalised on yet more slack defending when Makino, unmarked on the back post, prodded home a loose ball from a corner on 68 minutes to make it 3-0.
And four minutes from time, Brazilian forward Silva was afforded plenty of space when he raced clear and beat Janjetovic on his near post from the edge of the box.