World number nine Holger Rune said his brief collaboration with Andre Agassi had given him a unique insight into how the eight-times Grand Slam champion viewed the game and hopes to use the advice he received to take his game to the next level.

Rune announced himself as one of the sport's most promising young talents three years ago by winning his first Masters title in Paris after beating four top-10 players and defeating Novak Djokovic in the final.

However, the 22-year-old has had limited success since, winning just two more titles and failing to advance beyond the quarter-final stage at the Grand Slams.

With fellow young guns Carlos Alcaraz and Jannik Sinner now dominating the game's biggest events, Rune turned to American great Agassi earlier this month in Washington for a three-day training block.

"It was insane. I've never met a guy who sees tennis that way and I found it interesting," Rune told the Tennis Channel at the Canadian Open in Toronto.

"He makes things simple on the court. Sometimes tennis can be a difficult sport and sometimes it can be a very easy sport. There's always a reason why it's this or that.

"Some of the advice he gave me was very helpful. To share those three days, for him to get a look at my game, it was just amazing. My coach Lars (Christensen) appreciated it too, they talked a little bit and we're still in touch."

Rune said Agassi's tactics had struck a chord with him even though the Dane never watched him play growing up.

"I've watched so many YouTube clips with him on how he was taking the ball early," Rune added.

"It was so clear to see how he was making life easy for himself on the court ... it was a bit before my time so I didn't grow up watching Andre. But to look back at how tennis was then was really interesting to see."

Rune beat Giovanni Mpetshi Perricard in Toronto and next plays Alexandre Muller as he builds up for the August 24-September 7 U.S. Open.