At the helm of Montreal, Henry's Impact came from behind to beat the New England Revolution 2-1 on the opening day of the MLS season.
The Arsenal great's side had fallen behind after just 13 minutes at Stade Olympique, where Teal Bunbury volleyed in a Cristian Penilla cross.
However, Romell Quioto headed in from close range to bring Montreal level just eight minutes before half-time.
And the hosts found an 80th-minute winner as Maximiliano Urruti spectacularly lobbed stranded New England goalkeeper Matt Turner.
Hernandez made his LA Galaxy debut in a 1-1 draw away to the Houston Dynamo.
The former Manchester United and Real Madrid forward played 90 minutes as Houston came from behind, Mauro Manotas cancelling out Cristian Pavon's opener.
Atlanta United spoiled Nashville SC's first MLS game with a 2-1 victory at Nissan Stadium.
Walker Zimmerman scored Nashville's first goal to cancel out Ezequiel Barco's opener, but Emerson Hyndman's 37th-minute strike proved to be the winner in front of a crowd of 59,069.
Elsewhere, Oswaldo Alanis' brilliant 95th-minute free-kick helped the San Jose Earthquakes hold Toronto to a 2-2 draw.
The Colorado Rapids recorded a 2-1 win over DC United, Dallas beat Philadelphia Union 2-0, Orlando City and Real Salt Lake played out a 0-0 draw and Sporting Kansas City overcame the Vancouver Whitecaps 3-1, with record-signing Alan Pulido scoring on his debut for SKC.