The 19-year-old Tiafoe, number 101 in the world, took the in-form Federer to a first-set tie break before losing the second set 6-3 in their second round contest.

Federer, an 18-time Grand Slam champion, was hugely impressed by the way the Maryland youngster approached the match.

"I think the question was always how was he going to come out. It's the question also for any player. Also for me. How can you start a match? Seemed to be fearless, no problem, good serving, taking the ball early, making the plays," said the Swiss.

"That's what I like to see, when a younger player comes out, that he really feels he has nothing to lose and he's only got stuff to gain.

"I hope he's going to learn a lot from a match like this just because playing on a center court with a lot of people, under pressure, saving break points, making break points, playing breakers - that's what it's about.

"And it should feed a player like him with a lot of energy moving forward hopefully," added Federer.

Tiafoe is the son of immigrants from Sierra Leone and grabbed the attention of American tennis aficionados when he won the Orange Bowl junior competition at the Key Biscayne venue of the Miami Open as a 15-year-old.

Tiafoe was the youngest winner of the prestigious tournament and at 17 he entered the French Open on a wildcard. In January he won his first match in a Grand Slam event, beating Mikhail Kukushkin in the Australian Open.

Federer said he was not surprised by the American's powerful serve and hard hitting.

"I've hit with Frances maybe twice before: once at the French and once at the US Open. There he surprised me. I'm not going to get the surprise really a second time around because I saw the power he had, the explosivity he had. You know, how he easily can generate pace," he said.

"So I think he's going to be really good," said Federer who said he was impressed with the current crop of emerging young players on the tour.

"They're pushing each other up right now. They have a good dynamic. They are quite friendly also with one another yet they have good rivalry," he said.