Thursday's international friendly against Costa Rica saw England bag a 2-0 victory - their tenth consecutive match unbeaten.
Rashford in particular shone, scoring a sensational goal playing with a "swagger" that impressed Southgate, a world away from recent performances at his club, Manchester United.
Though perhaps a better problem to have than others experienced by England managers in recent years, the performance presents something of a quandary for Southgate, posing the difficult question: should Rashford start over Manchester City's Raheem Sterling?
What Sterling doesn't do
Speaking on ITV after the performance Ian Wright gave Rashford his seal of approval, saying: "I'd go with Rashford because that's exactly what we need from a second striker - I love him there."
He added: "Rashford took his opportunity. He got half a yard and bang. That's what Harry Kane does and what, unfortunately, Sterling doesn't do."
Match commentator, former England manager Glenn Hoddle also spoke highly of him.
He said: "I'd like to see him up front against Tunisia. You wouldn't want to play against him and Kane."
The Times' Chief Football Writer Henry Winter wrote: "It takes something special for Elland Road to embrace and salute a Manchester United player and Rashford certainly delivered something special here."
He added: "He [Rashford] shone in the Raheem Sterling role, playing off the centre forward, in this case Jamie Vardy, yet it would still be a surprise if he usurped Sterling. He represents an exceptional understudy."
Former-England player and Match Of The Day presenter Gary Lineker pronounced Rashford's goal simply as "stunning," describing the youngster as "a prodigious talent."
Writing for The Guardian, Barney Ronay commented: "There was something heartening about seeing him [Rashford] play with such freedom so soon after the scolding he received on FA Cup final day. Gareth Southgate has been a significant positive influence."
Former England player and 5Live pundit Chris Waddle also came down on the side of Rashford.
He said: "If you look at Sterling, he gives the ball away a bit more in easy positions and I think Rashford plays better in an England shirt. "Even though Rashford is younger, he's more consistent."
Cristian Gamboa of Costa Rica tackles Marcus Rashford of England during the International Friendly match between England and Costa Rica
Image credit: Eurosport
Speaking after the match, Southgate told 5Live Rashford was "desperate to do well."
Though he wouldn't be drawn on whether or not he had already decided his starting XI for England's opener against Tunisia on June 18, Southgate said: "We have got great competition for places throughout the team - you saw that tonight. We've a decision to make for the first game."