Tottenham's Europa League hopes have been dealt a blow after Jeremy Perbet's goal gave Gent a surprise victory in their last-32 first-leg meeting.
French striker Perbet controlled and slotted into the corner from Danijel Milicevic's pull-back on the hour.
A strong Spurs line-up were poor for most of the evening, although Harry Kane clipped the post after half-time.
Gent, eighth in the Belgian league, almost added a second as Milicevic's shot was tipped on to the post.
The second leg is at Wembley on Thursday, 23 February.
Spurs stutter to surprise defeat
Gent's 20,000-capacity stadium, the Ghelamco Arena, is host to a Michelin-starred restaurant, but there was little to feast on for Tottenham, who turned in a strangely listless performance.
Mauricio Pochettino had spoken before the match about how keen his players were to put behind them a poor display in losing 2-0 at Liverpool in the Premier League on Saturday.
With that in mind, Pochettino selected a very strong side - with only two changes to the team beaten at Anfield.
Dele Alli skimmed an early shot wide from just outside the penalty area after good build-up involving Harry Winks and Ben Davies, but that was as good as it got in the opening half.
Pochettino's decision to move midfielder Moussa Sissoko out to the left at half-time led to a lively spell from the visitors, during which Kane clipped the post.
But Sissoko looked increasingly lost, and the Tottenham head coach was prompted into more tactical tweaks in an attempt to find an equaliser.
Nothing worked - and Tottenham's frustration was summed up as Alli picked up a needless yellow card for dissent.
Wembley worries ahead for Pochettino
Gent's fans were singing "we're going to Wembley" during the second half, in anticipation of next week's second leg at England's national stadium.
They may have more reason than Tottenham to look forward to their big night in north London.
Spurs stumbled at their temporary European home in this season's Champions League - failing to qualify from their group after losing at home to Monaco and Bayer Leverkusen.
Unless they find a way to make themselves more comfortable at Wembley, their hopes of European success will end with next week's second leg.
Perbet proves a pointGent initially posted a team line-up on Twitter with 12 players - Israeli centre-back Rami Gershon having been added by mistake
Gent boss Hein Vanhaezebrouck - celebrating his 53rd birthday - caused something of a surprise with his team selection, making five changes and leaving his 15-goal top scorer Kalifa Coulibaly on the bench.
It suggested that Vanhaezebrouck is prioritising a top-six place that would secure qualification for the Belgian league championship play-offs above European progress.
Yet his decision to select the 32-year-old journeyman Perbet in attack paid off handsomely.
Even before Gent took the lead, the players selected were full of energy, pressing Tottenham into mistakes and enjoying plenty of possession.
They created decent openings; centre-back Samuel Gigot shanked an effort wide from the edge of the penalty area, while Toby Alderweireld had to block a shot from midfielder Kenny Saief, who made an adventurous run from the left after a poor Kyle Walker pass.
Better chances came after half-time, with Milicevic slicing wide as Spurs switched off at a throw-in moments before Perbet's goal, and unmarked centre-back Stefan Mitrovic spurning an opportunity to make it 2-0 as he headed over from a corner.
Before next Thursday's second leg at Wembley, Tottenham visit Fulham in the fifth round of the FA Cup on Sunday, when Gent travel to fellow mid-table side Standard Liege in the Belgian league.