Messi and Ronaldo have both made history during the tournament, with Argentina captain Messi scoring twice in a 2-0 win over Austria to move past Miroslav Klose's previous record and reach 18 World Cup goals.
Portugal forward Ronaldo also created history by scoring twice against Uzbekistan, becoming the first player to find the net at six different World Cups.
Former Liverpool manager Klopp admitted he had been impressed by the determination shown by both players as they continue to perform at the highest level late in their careers.
"As a mere spectator, it naturally captivates me a bit because they are the best players of the last 10, 15 years," Klopp said.
The German coach highlighted Ronaldo's response after facing criticism following Portugal's opening match, praising the forward's mentality and desire to improve despite being 41 years old.
"What was great to see was this: after the first game, in which Cristiano Ronaldo was heavily criticised, to then strike back like that, and at 41 years old with an extremely lively, intense performance, I was very pleased," Klopp added.
"The fact that he's still so bothered at his age when something doesn't work out is extraordinary, and his reaction is all the more impressive."
Klopp also spoke about the unique experience of watching Messi compete at another World Cup, describing the Argentine's presence as something special.
"It's extraordinary that we get to experience this generation. It's special," he said.
Messi now has 18 World Cup goals, while Ronaldo has scored 10 in the competition as Argentina and Portugal continue their push towards the knockout stages.
Argentina will face Jordan and Portugal will meet Colombia in their final group-stage matches on Saturday, 27 June.
