Lam laid on two tries, had a hand in several others and landed one booming 40/20 from inside his own 20m line to add a touch of extra class in a superb performance.
The 25-year-old former Sydney Roosters playmaker continued his stellar form from the Challenge Cup final when he guided Leigh Leopards to victory and won the Lance Todd Trophy as man of the match.
The Test match was delayed for 10 minutes inside the opening minute of the game as medical staff attended Cook Islands half Tevin Arona.
Arona injured his neck while making a tackle and was put in a brace and stretchered from the field.
The Cook Islands lacked organisation from that moment and the Kumuls turned it on.
The Gold Coast recently extended second-rower Jacob Alick's deal until the end of 2024 and it was evident why when he offloaded under pressure to send North Queensland centre Zac Laybutt over out wide for a 4-0 lead.
Laybutt then caught and passed the ball in one flowing movement to send winger Robert Derby in to score.
Props Epel Kapinias and Valentine Richard crashed over. Lam set up Macdonald with a cut-out pass for his first try, before an Alex Johnston bust led to Laybutt's second on the cusp of halftime for a 30-0 lead.
Macdonald scored two more tries inside the opening three minutes after the break to put the result beyond doubt but the Cook Islands kept trying.
Their fullback Esom Ioka scored the individual try of the day when he dived full stretch to catch a Brad Takairangi bomb and score.
It was fitting that Lam set up Macdonald for his fourth try for the Kumuls just before fulltime.
St George Illawarra forward Jack de Belin played strongly in his debut for PNG, who were coached for the first time by former Titans mentor Justin Holbrook.
