The 25-year-old midfielder's display showed a wider audience why his Aston Villa boss Dean Smith said he would build a side round him after he signed a new contract prior to this season.
The praise for Grealish was a useful distraction as England suffered back-to-back competitive defeats for the first time since September 2018, posing further question marks over Southgate's change of formation.
The coach's switch from a 4-3-3 formation that saw the Three Lions score 37 goals in eight games in qualifying for Euro 2020, to a 5-2-3 has reaped just three goals in five Nations League games.
Southgate eulogised about Grealish after he started for the first time in a competitive match.
"I just thought he was outstanding and he should be delighted with the way he played," said Southgate.
"Today was a great game to see him at that level and I couldn't speak highly enough of his performance."
Former Tottenham Hotspur defender Graham Roberts said Grealish's performance reminded him of his former team-mate Paul Gascoigne.
Another former Spurs star, Gary Lineker, tweeted "I love watching Jack Grealish, such a delightful footballer."
Grealish's performance attracted praise too from abroad with Monaco's former Arsenal star Cesc Fabregas purring in a tweet : "Great personality Jack Grealish (with an applause icon)."
The British media contrasted the positives of Grealish's display with the overall performance of an England side lacking in spark, with forward Harry Kane getting few scoring chances.
"On a sobering night for England, on an evening when they were reminded of the importance of being clinical, and basically given a lesson in control by Belgium, there was only one uplifting element, Grealish's fearlessness," opined The Times.
"There was one moment in the second half, with England second best, that Grealish evoked memories of Paul Gascoigne."