Lukaku, his country's record goalscorer, was introduced in the 66th minute in Seattle on Monday (Tuesday AEST) and within seconds was involved in the move that saw Mohamed Hany prod in an own goal to bring the two-time semi-finalists back on level terms.
Egypt had started brightly and snatched the lead in the 20th minute when Emam Ashour lashed the ball past Thibaut Courtois from the edge of the box to give his side hope of a first ever win at a World Cup finals.
Belgium looked flat-footed for much of a first period in which they failed to fashion a shot on target, and the African side looked more likely to add to their lead with Mostafa Ziko bringing a fine save out of Courtois on the half-hour mark.
Belgium stepped up the pace after the interval and came close to a leveller when Kevin De Bruyne lashed a free kick against Egypt goalkeeper Mostafa Shobeir's right-hand post after a foul on Jeremy Doku.
Ashour snatched at a great chance to double Egypt's advantage before Belgium came closer, Youri Tielemans lashing just wide from his side's first corner on the hour mark, then De Bruyne scuffing at a fine chance from the centre of the box.
Lukaku, dubbed "out of shape" by Belgium coach Rudy Garcia despite including him in his World Cup squad last month, made an instant impact as he hustled the unfortunate Hany into poking the ball into his own net in the 66th minute.
Both sides pressed for a winner in an absorbing contest, with Shobeir acrobatically tipping away a drive from Brandon Mechele, and teenager Hamza Abdelkarim not far from connecting to Karim Hafez's deep left-wing cross.
