West Ham midfielder Rice earned widespread praise for his performance on his full England debut against Montenegro on Monday.
The 20-year-old only became eligible for the Three Lions earlier this month after switching his allegiance from the Republic of Ireland and immediately looked at home on the international stage.
While Rice was making just his second appearance in an England shirt, Liverpool skipper Henderson came off the bench in Podgorica to earn his 50th cap.
But, according to Merson, it was Rice who impressed rather than his more experienced midfield partner.
"It’s the hardest thing in football for a midfielder to keep it simple and not get carried away when you play in that position," Merson told the Daily Star.
"So many midfielders start off well, winning the ball and playing it simple, and then they get carried away and start trying to spray Hollywood passes everywhere.
"Jordan Henderson does it all the time. But not Declan Rice. He just kept getting it and giving it. He always found the right pass.
"That shows massive maturity for someone so young. It was really impressive. It might sound simple, being able to do that. But people don’t realise how much discipline it takes.
"Fernandinho is brilliant at it for Manchester City. He never over-elaborates. For a kid of his age to play like that on his England debut is outstanding.
"I thought [Rice] was man of the match against Montenegro. He never chased the game and when he lost it he won it straight back."
Rice’s performances for club and country this season have not gone unnoticed, with Manchester City among a number of sides believed to be tracking his progress.
West Ham boss Manuel Pellegrini has already admitted that Rice’s future is “a matter of price” and Merson feels the youngster’s days at the London Stadium are numbered.
"The trouble for West Ham is he’s not on much money there and I don’t see how they keep hold of him if City or United come in for him,” added Merson.
“Hammers fans need to enjoy him while he’s still there.”