Harden lasted less than a minute before being forced from the court with a right hamstring injury.
Although the Nets took a quarter to adjust, Kyrie Irving and Kevin Durant found their rhythm in the second period and did not let up from there, combining for 54 of Brooklyn’s points.
They were ably assisted by Blake Griffin who contributed 18 points and 14 rebounds on four-for-nine three-point shooting.
Although the Bucks dominated in the post, they struggled heavily from range, shooting just 20 per cent from beyond the arc.
Giannis Antetokounmpo led the way for the visitors with 34 points and 11 rebounds.
Game two is back in Brooklyn on Tuesday.