The Lille midfielder was teed up by Burak Yilmaz before blasting in from long range on the stroke of half-time, with PSG unable to make its possession count from there on in.
The story of the final could have been different, however, had Abdou Diallo taken the best second-half opportunity, failing to convert a headed effort from inside the six-yard area with just Leo Jardim to beat.
After dethroning the capital side as Ligue 1 champion last season, Jocelyn Gourvennec's side has now collected the first piece of silverware of France's domestic season, with the showpiece event taking place in Israel this year.
Yilmaz's drilled free-kick seemed destined to open the scoring inside 10 minutes, though Keylor Navas's fingertip save pushed the effort wide of his left-hand post.
PSG, hampered by big-name absentees, including Kylian Mbappe and Neymar, dictated proceedings for the remainder of the first half, yet only Julian Draxler tested Jardim as he fizzed from range to force the goalkeeper into a smart save.
Yilmaz worked Navas once more on the counter, but it was Xeka who broke the deadlock as he powered in a right-footed effort from just outside the area.
Diallo should have restored parity with a close-range header but somehow managed to nod wide after Mauro Icardi had redirected the ball towards the left-back.
Icardi thought he had levelled things up with 15 minutes to go but his chipped finish was ruled out for offside, while Draxler volleyed inches wide moments later as PSG drew a blank.