Wiegman's Lionesses beat Belgium to keep their Olympic dream alive
Belgium had entered the contest as Nations League Group A1 leaders but sank to third by full-time as the Netherlands beat Scotland 4-0 to go top, while the Lionesses moved up to second.
The group winners will progress to the semi-finals with a place at the Paris 2024 Games the prize for the two finalists.
Hemp pounced after the Red Flames failed to clear a corner to score the only goal after just 13 minutes.
Thereafter, it was a tale of missed opportunities for Sarina Wiegman's women.
Alessia Russo twice missed big chances to double England's lead, but they held on to inflict Belgium's first loss in the group.
"We started the game really well, with a lot of pace and looked dangerous straight away," said Wiegman.
"Our tempo dropped in the second half and they then looked dangerous. It is just a lot easier when we score more and make it more comfortable."
The two sides meet again in Leuven on Tuesday and England can ill afford any slip-ups if they are to keep pace with the Dutch.
The Netherlands travel to Wembley in December in what could be the group decider before England finish their campaign with a trip to rivals Scotland.