However, the Saudi side's evening was soured by a late injury to Neymar.
Al-Ahli's Roberto Firmino and Riyad Mahrez ensured it was a positive evening for Saudi Pro League sides in the recently revamped continental competition, with both netting twice in a 5-1 thrashing of Iraq's Al-Shorta in Jeddah.
Iran's Persepolis drew 1-1 with Al-Gharafa from Qatar, and Al Wasl of the United Arab Emirates also shared a 1-1 draw with Qatari outfit Al-Sadd.
Al-Hilal and Al-Ahli have now won all four of their games in the league phase of the competition and opened up a four-point gap over third-placed Al-Sadd, with fellow Saudi Pro League side Al-Nassr a further point back in fourth.
Cristiano Ronaldo's side Al-Nassr meet holders Al-Ain on Tuesday, when Uzbekistan's Pakhtakor take on Al-Rayyan of Qatar.
The first eight finishers in the 12-team league phase in both west and east Asia will advance to the knockout rounds in March.
Mitrovic put Al-Hilal ahead at Riyadh's Kingdom Arena with a 15th minute tap-in, and doubled the advantage with another straightforward finish in the 33rd minute.
The former Fulham striker completed his hat-trick with a 74th-minute header into the bottom corner from Joao Cancelo's cross from the right.
However, the evening ended on a sour note for Al-Hilal when Neymar, who returned two weeks ago from a year out with a ruptured cruciate ligament, was replaced 29 minutes after his introduction from the bench due to injury.
In Jeddah, Firmino opened the scoring when he headed in Ziyad Al-Johani's 14th-minute cross, but after Franck Kessie saw his penalty saved by Ahmed Basil, Sajjad Jasim levelled on the counter for Al Shorta.
Firmino restored his team's lead in first-half injury time from three yards, then set up Feras Al-Brikan to score Al-Ahli's third also from close range eight minutes into the second half.
Mahrez slotted the fourth into the bottom corner in the 61st minute, then added his side's fifth four minutes later.
Romain Saiss earned a point for Al-Sadd in Dubai, equalising for the Qatari outfit just after the hour in their draw with Al-Wasl to cancel out Alexis Perez's deflected 29th-minute opener.
Substitute Ahmed Al-Ganehi levelled for Al-Gharafa, also in Dubai, three minutes after Farshad Faraji had given Persepolis a 53rd-minute lead as the pair shared the points. Â