Gatland's father Warren looked set to celebrate victory and spoil the party at a buoyant Forsyth Barr Stadium, where supporters were jubilant throughout, New Zealand's government having lifted restrictions this week after declaring the country no longer had any known active cases of coronavirus.
But Damian McKenzie's close-range drop goal to put the visitors ahead in the 78th minute was met with an immediate response as the Highlanders' replacement full-back nailed a response from 40 yards.
Aaron Mauger's men rose to a special occasion from the off, with Ash Dixon the beneficiary of a well-constructed lineout drive in the 16th minute.
Rob Thompson found a wonderful line off a short pass from scrum half Aaron Smith to set up his fellow centre Sio Tomkinson, Mitch Hunt's conversion opening up a 15-6 lead for the Highlanders midway through the first half.
The Chiefs found a brilliant response, with Sean Wainui released by Quinn Tupaea to touch down and McKenzie adding the extras from out wide.
Debutant Vilimoni Koroi was sent to the sin bin for a tip tackle on Naitoa Ah Kuoi but number eight Marino Mikaele Tu'u made light of the Highlanders' numerical disadvantage by going over to cap a thrilling half.
After the break, the new rules concerning the breakdown meant frequent penalty infringements and a fracturing of the game's earlier pleasing flow.
Jona Nareki became the second Highlanders man to visit the bin and Anton Lienert-Brown brought the Chiefs to within a point with eight minutes to play.
McKenzie, who finished with 17 points, dragged his conversion wide before responding in style as he looked to have become the matchwinner. However, Gatland Jr had other ideas.