Faiz Selemani restored parity after Mitrovic's 15th-minute opener at Prince Faisal bin Fahd Stadium, only for Jorge Jesus' hosts to roar back and be crowned champions with three games remaining.
Ahmed Al Juwaid's own goal handed the initiative back to the dominant Al Hilal, who led 4-1 at the break after Mitrovic added another to his tally and Sergej Milinkovic-Savic was on target.
The second of Mitrovic's strikes took him to a team-leading 26 league goals this term as Al Hilal breezed to another title, moving an unassailable 12 points clear of Cristiano Ronaldo's Al Nassr.
Jesus' side are unbeaten through all 31 games this season after securing their record-extending 19th top-flight crown in history, while Al Hazm need to win their last three matches to have any chance of staying up.
Al Hazm's relegation rivals Al Tai boosted their chances of survival in Saturday's earlier clash after a 1-1 draw away against Al Raed.
Al Tai are just a point away from 15th-placed Abha Club in their bid for top-flight safety after Ibrahim Al Nakhli's strike was cancelled out by Al Raed's Mohammed Fouzair in the second half.
Mohammed Fouzair equalised from the spot at the start of the second half, cancelling out the 39-year-old's first-half goal at Al Awal Park on Thursday.
Al-Nassr dominated the opening exchanges, and when the visitors struggled to clear their lines from a corner, Ronaldo towered over everyone in the box to nod home Sadio Mane's delivery.
They found themselves on the backfoot minutes into the second half though - Amir Sayoud's curling shot was saved, but Fouzair was dragged back by Aymeric Laporte when he tried to reach the rebound, resulting in the defender receiving a straight red card.
After a VAR review, the card was downgraded to a yellow and a penalty was awarded to Al-Raed. Fouzair then made no mistake from 12 yards, picking out the bottom-right corner.
Talisca struck the post as Al-Nassr searched for a winner, and Ronaldo thought he had found one with just under 15 minutes left. He curved his run in behind the defence to poke past Meshari Sunyur, who had looked unbeatable, but the forward was offside, and it did not count.
The hosts were unable to join Al-Taawoun on three points at the top of the table after their win earlier on Thursday.
Data Debrief: Fine margins deny Ronaldo
After suffering disappointment in the Saudi Super Cup last weekend, Al-Nassr would have been keen to get off to a winning start in the league.
And they came close. They dominated throughout the game, having 28 shots to Al-Raed's seven, generating 2.18 expected goals.
Ronaldo now has 36 goals in the Saudi Pro League and was denied a 37th by the closest of margins in a frustrating day for the hosts.
