The reigning champions had to wait five days to start their campaign but produced an ominous performance that doubled as the biggest win in tournament history, surpassing Germany's 11-0 trouncing of Argentina in 2007.
Morgan took her goal tally at international level to 106 with her well-taken haul, while Samantha Mewis added a double and was involved in setting up another two goals.
Jill Ellis' side had the three points in the bag with a 3-0 lead at half time but impressively, they did not let up after the break against a Thailand side who were well and truly out of their depth, the second half ending in truly embarrassing fashion for the underdogs.
5 - Alex Morgan is the second player in #FIFAWWC history to score five goals in a single game, doing so 27 years and 199 days after fellow @USWNT international Michelle Akers managed this feat against Chinese Taipei in November 1991. Decimated. pic.twitter.com/kkl7kay7Rz— OptaJoe (@OptaJoe) June 11, 2019
An offside decision cost Morgan a fifth-minute opener but the prolific forward would not be denied, nodding in Kelley O'Hara's dinked cross with aplomb to open the scoring.
Morgan was involved in the second goal, too, playing a neat one-two with Rose Lavelle before the latter produced a 20-yard effort that Thailand goalkeeper Sukanya Chor Charoenying could only fumble into the back of the net.
Lindsey Horan got her side's third, reacting quickest to a goalmouth scramble to fire into the roof of the net, and only an incredible sequence of play - featuring a host of last-gasp blocks, a smart Chor Charoenying save and a penalty appeal – kept the margin to three at the break.
The floodgates opened early in the second half, though, as a hapless Thailand side conceded four goals in a six-minute period.
Mewis started things, getting the goal her terrific performance deserved with a deflected effort, before Morgan prodded home the fifth at the far post.
Mewis then made it six goals in her last five appearances for the national team when she pounced on a loose ball and soon turned provider as Lavelle swept in a cross.
Morgan's hat-trick effort was a stylish goal, with quick feet winning her the space to fire in an excellent 15-yard finish, and Megan Rapinoe then finished smartly to end a fast break in style.
A fourth goal was to follow for Morgan, who rounded off her brilliant night with a fiercely hit fifth after Mallory Pugh had got on the scoresheet. Carli Lloyd capped off the night with the final goal in injury time, a three-minute period that must have felt like three hours for the Thailand players.