Inter were 3-0 up after 40 minutes thanks to two goals by Maurizio Ganz and one from Chile's Ivan Zamorano and seemed well on course to cruise into the final.
That seemed even more likely when the Monaco defender Gilles Grimandi was sent off at the start of the second half for a punch. However, in the 71st minute, substitute Ikpeba conjured up a precious away goal with a superb long-range shot with almost his first touch of the ball.
"I'm happy enough about the result but I'm more concerned about that late goal which puts our qualification at risk," Inter's English coach, Roy Hodgson, said. "Now we have to avoid losing 2-0 in Monaco," the Blackburn- bound Hodgson added.
Jean Tigana, the Monaco coach, fuelled Hodgson's fears. "In the return leg, it will be a different Monaco," he pledged.
Certainly, in the first half, Monaco looked a pale shadow of the side that had won all of its previous away ties in this season's Uefa Cup competition. The runaway French League leaders could not come to terms with Inter's aggression and ability to turn defence into counter-attack.
As early as the 10th minute, England's Paul Ince put Zamorano free but the Chilean dragged his shot wide.
In the 14th minute, the Inter defender Salvatore Fresi was unlucky not to give his side the lead when he saw his header from the six-yard box cannon back off the body of the Monaco goalkeeper Fabien Barthez.
Within three minutes, Ganz had made amends. Released on the left by a defence-splitting pass from Zamorano, Ganz raced into the penalty area to beat Barthez with a fierce right-foot shot.
Thirteen minutes later, Ganz repeated the feat from the other side of the penalty area, although this time the provider was the inspirational French playmaker Youri Djorkaeff. It took Ganz's tally in this season's Uefa Cup to eight.
As Monaco pushed forward they exposed themselves to another counter-attack and this time Ganz turned provider, laying on an inch-perfect cross that left Zamorano with a simple tap-in.
Soon reduced to 10 men Monaco looked down and out but in the 71st minute Ikpeba gave his side a lifeline.
There appeared no apparent danger when the Nigerian, an Olympic gold medallist, picked the ball up on the right wing, but he cut inside and unleashed a shot into the top corner that gave Gianluca Pagliuca no chance.
The goal fed fresh life into Monaco's tiring legs and in the dying minutes they came close to adding a second, giving warning that this tie is not over yet.
Internazionale: Pagliuca; Pistone, Paganin, Fresi, Bergomi, Ince, Sforza (Winter, 78), Zanetti, Djorkaeff, Ganz, Zamorano.
Monaco: Barthez; Blandeau, Grimandi, B Irles (L Irles, h-t), Petit, Legwinski, Djetou, Benarbia (Ikpeba, 69), Collins (Scifo, 62), Anderson da Silva, Henry.Reuse content