The Angolan prevailed in the #41 WRT ORECA-Gibson 07 alongside Louis Deletraz and Robert Kubica thanks to a four-second shorter final pitstop than erstwhile leader Tom Blomqvist's #22 United Autosports ORECA.
In a race disrupted by four safety cars, the #41 crew was hampered by the timing of the third when Jacques Villeneuve's Vanwall Hypercar clashed with the GTE Am Ferrari of Francesco Castellacci, as Kubica was forced to take on emergency fuel and then pit again immediately after the race returned to green flag conditions.
However Kubica managed to save a lap of fuel relative to United driver Oliver Jarvis prior to their penultimate stops, which helped to ensure a quicker splash-and-dash when Blomqvist led Deletraz in 12 minutes from the end.
In what Andrade reckoned was "a hard race to follow for everybody", he told Motorsport.com that the various strategy permutations were not clear until the final throes of the race.
"I didn’t really think we could win the race up until 12 minutes from the end, really, when we saw the strategy," he said.
"At one point we thought that United would win the race, at one point we thought Inter Europol would win the race because they anticipated the pitstops.
"At one point we thought the #31 sister car would win the race by a lap because they had a whole lap on the field when the safety car came out before the pass around.
"But only at the very end when we realised the gap to the Inter Europol stabilised and obviously every lap that went by our splash of fuel would be less and less.
"So as that gap stabilised we knew they were no longer a threat and then it became a real possibility that we could actually win the race because Louis did an amazing job and caught up a lot to Tom Blomqvist and we had one last lap of fuel.
"Actually when we both boxed at the same time, this is the last thing we wanted because we wanted to box preferably one lap before or after them.
"We thought if Louis could have one clear lap we could get the race win through there. But it was crazy how the race panned out."
Andrade admitted that he "completely bottled the start" from second on the grid alongside Blomqvist, dropping to ninth after locking up into La Source, before recovering to third at the end of his opening double stint.
Blomqvist had built up a 45-second lead before Renger van der Zande's frightening crash resulted in a safety car that eradicated his advantage, with Andrade conceding "we all just assumed we were out of the race contention because we were so far back".
"We were more than a minute behind the leaders at this point," he said.
The second #31 WRT entry of Ferdinand Habsburg, Robin Frijns and Sean Gelael exchanged the lead several times with Deletraz during the middle phase of the race but ultimately faded to fifth.
Team boss Vincent Vosse conceded that the many interruptions hampered its strategy.
"At the end I would say everything was not perfect and I think it was not perfect for anyone," he told Motorsport.com.
"It would be nice to say everything was under control but of course, it’s almost impossible to have everything under control.
"We had two quick cars, at one stage we were first and second, but it’s impossible to read all the race."
