The Brazilian forward mesmerised for Los Blancos and reached 18 goals across all competitions this season, while Dani Carvajal and Brahim Diaz also found the net in an entertaining romp for Carlo Ancelotti's side.
Girona, second, were undone by Yellu Santiago's first half strike and have now suffered four consecutive away defeats -- started by a demoralising 4-0 thrashing at Madrid.
Third-place Barcelona, 11 points behind Madrid, travel to face Atletico Madrid, fifth, and can overtake Girona with a victory on Sunday.
Athletic Bilbao rose above Atletico to fourth with a 2-0 win over Alaves thanks to a brace from Gorka Guruzeta.
Madrid were without top goalscorer Jude Bellingham, completing a two-match suspension but, with Vinicius in full flow, barely missed the England international at El Sadar in Pamplona.
"I congratulated him, he had an extraordinary game, he made good decisions, he moved very well without the ball, that's where's he's improved the most," Ancelotti told reporters.
"With the ball he's always efficient and without it he's spectacular at the moment, he's so fast."
Vinicius' name made headlines this week after Real Madrid filed a legal complaint over alleged racist insults aimed at the Brazilian by Atletico Madrid and Barcelona fans, but on the pitch the forward's quality continues to speak for itself.
The 23-year-old dispossessed Alejandro Catena, ran through and calmly rolled the ball past Sergio Herrera to break the deadlock after four minutes.
Osasuna were quickly back level through Ante Budimir, who finished from close range at a corner.
Madrid captain Carvajal put his side in front again in the 18th minute, finishing sublimely with the outside of his boot after Fede Valverde cleverly hooked the ball into his path in the box.
Vinicius was booked just before half-time for dissent, his fifth yellow card of the season in La Liga -- meaning he is now banned for Athletic Bilbao's visit to the Santiago Bernabeu at the end of March.
Diaz stretched Madrid's lead after an hour with a clinical finish after running on to a long ball, flicked on by Valverde.
'Pressure'
Vinicius grabbed his second a few minutes later with a subtle poked finish after Valverde sent him hurtling in on goal to complete a hat-trick of assists -- it was the striker's 12th league goal of the season.
He started the campaign slowly by his high standards but has six goals in his last four league matches.
The Brazilian could have completed his hat-trick just a couple of minutes later but fired wide after another dart into the box past Osasuna's crumbling back line.
Home fans whistled Vinicius as he was substituted in the final stages but Ancelotti gave the forward a hug as thanks for taking Madrid one step closer to the Spanish title.
"The pressure that he has in terms of the atmosphere, he has to control that a bit more," added Ancelotti, after Vinicius' booking, his third yellow in three league games.
Iker Munoz pulled one back for Osasuna in stoppage time before Madrid almost wrapped up the win in spectacular fashion, but youngster Arda Guler hit the bar with an effort from just inside Osasuna's half.
'No words'
Getafe, despite the absence of top goalscorer Borja Mayoral, were able to inflict a fourth consecutive away defeat on Michel Sanchez's slumping Girona.
"Every defeat worries us, we want to fight to get into the Champions League," Michel told reporters.
"We have a historic chance to do it and if we don't, for me, it would be very tough to take."
The Catalan minnows' top goalscorer Artem Dovbyk missed two good chances after Santiago fired Getafe ahead following good work by Ilaix Moriba.
"I have no words to describe this defeat," said Girona winger Savinho.
