Irish manager Carla Ward had spoken of her expectation that Belgium would come flying out of the blocks in Leuven after they were blown away by the Irish in Dublin.
But it was the Republic who should have taken an early lead when an unmarked Caitlin Hayes sent a header wide from McCabe's cross.
Belgium, who defeated European champions England in the Nations League in the spring, grew into the game and began to pile pressure on, but the visitors had another chance to take the lead when Nicky Evrard spilled the ball in the area from a corner.
Hayes' header found Aoife Mannion, whose powerful drive was touched by the recovering Belgian goalkeeper before Jarne Teulings hacked the ball off the line.
But Belgium took the lead on the night through Wullaert, who finished a flowing Belgian move in the 33rd minute.
There was some neat play and Laura Deloose's low ball to the back post found Wullaert and the captain swept the ball into the bottom corner.
Things got even better for the hosts when Wullaert grabbed her second of the game five minutes before the break.
Hayes gave away possession just outside the area and the in-form Inter Milan forward spotted Grace Moloney off her line and lobbed the ball over the stranded goalkeeper and into the net.
Amber Tysiak headed wide early in the second half but from there it was the Republic who looked the more likely to get the crucial next goal.
Emily Murphy forced Evrard into a strong save and the PSV goalkeeper was called into action again from Marissa Sheva's low effort.
Larkin, minutes after coming on as a substitute, dragged an effort wide from a good position in the area, and Kyra Carusa called Evrard into action again with a low and powerful effort.
But Larkin would make up for that miss when the ball fell to her in the area and she showed superb composure to dink the ball over Evrard.
There was a late scare as Sari Kees hooked over from a corner, but it was the Irish players who were left to celebrate in front of the travelling support in Belgium.