Mallorca, who had lost just once at San Moix in nine league games prior to Barca's visit, almost levelled late on, but Jaume Costa saw his effort brilliantly saved by Marc-Andre ter Stegen. They remain 15th, four points clear of the drop zone.
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A COVID-19 outbreak among the Barca squad, coupled with injuries and suspensions, meant they travelled to Mallorca with just 11 first-team players available, including two goalkeepers.
Coach Xavi Hernandez called up eight B team players to make up the numbers, with Barca left particularly short in attack.
Ansu Fati, Memphis Depay and Martin Braithwaite were all missing with injuries, while Ousmane Dembele, Abde Ezzalzouli and Philippe Coutinho were among eight players to miss the match after testing positive for coronavirus. New signing Ferran Torres is not yet available.
De Jong, therefore, was the only first-team forward available and, flanked by youngsters Ferran Jutgla and Ilas Akhomach, he starred in an impressive first half from Barca.
"I feel delighted, really happy we won today, especially with my goal, which was important for the team. The most important thing is the win. It's been a tough first half of the season and it's a good step by winning this game today," De Jong said after the match."
Jutgla then curled just off target before De Jong twice struck the woodwork. The Dutch striker flicked a Jutgla pass onto the post before hammering a brilliant overhead kick off the bar.
De Jong's luck finally changed in the 45th minute. Reina came for Mingueza's cross but got nowhere near it and De Jong headed into an empty net.
"Luuk's an exemplary professional. There's talk about him leaving, but he works hard and sacrifices himself for the team," Xavi said after the match. "He's an amazing professional. I am happy with him. Of course I consider that he could stay, he was useful today. We will see in the future, everything is just a hypothesis for now."
Mallorca, who were missing four players through COVID-19 themselves, improved after the break as Barca handed debuts to two youngsters, Alvaro Sanz and Estanis Pedrola.
The home side threw everything forward late on, with Fer Nino heading over before Costa's late chance was beaten away by the arm of Ter Stegen as Barca held on for three points.
Barcelona's Eric Garcia praised Ter Stegen for his performance, saying: We owe 70% of the win to Ter Stegen."
He was spectacular. He's a top goalkeeper. We know he responds in moments like that. Mallorca were pressing and we knew we had to soak it up and we've shown we're able to do that."