Denmark striker Hojlund headed home the crucial goal with 12 minutes remaining at the Stadio Diego Armando Maradona.
The 22-year-old also put Napoli ahead early on in Naples, his first club goal since netting the winner against Genoa in early October.
Napoli are one point ahead of Inter Milan after condemning Juve to a first league defeat since Spalletti took charge of the Turin giants in late October, but will be surpassed on goal difference by AC Milan on Monday if the seven-time European champions beat Torino.
“All I can say is thank you, thank you, thank you to the players,” said coach Antonio Conte, who looked close to a shock exit after a dismal defeat at Bologna before the last international break.
But Napoli have won five on the bounce in all competitions since then – in the midst of an injury crisis – and next travel to Portugal to take on Sporting Lisbon in the Champions League on Wednesday.
“They’ve grown so much. It makes me very proud because they understand what we’re trying to do and the period we’re going through, and they respond in an incredible fashion,” added Conte.
Juve are now eight points off the title pace after 14 matches as Spalletti, who led Napoli to a first Scudetto in over three decades in 2023, struggles to get a tune out of his new players.
Juve had looked good for a result when Kenan Yildiz coolly rolled home his sixth goal of the season after brilliantly exchanging passes with Weston McKennie.
Juve had been the better team of the second half up to that point but failed to capitalise on that moment, with Yildiz’s substitution in the 76th minute being quickly followed by Hojlund’s winner. (AFP)