The US Open semi-finalist survived a championship point in the third-set tiebreak to seal a thrilling 4-6 ,7-6, 7-6 win over German Jan-Lennard Struff for his first grasscourt crown ahead of next month's Grand Slam at Wimbledon.

Tiafoe, who was born to immigrant parents who eventually settled in the United States after fleeing civil war in Sierra Leone in the 1990s, said reaching a career-high number 10 was something that he would never forget.

"Super emotional. For a guy like me, with my story and everything," said Tiafoe, who was exposed to the sport when his father worked as a caretaker at a tennis centre in Maryland.

"I'm a guy who shouldn't even really be here doing half the things he's doing, and now when you say his name, you can say he's top 10 in the world.

"So (that is) something that no one can take from you and I'm going to remember that forever. And hopefully, I can ride that for a long time."

Tiafoe's achievement means that he and number eight Taylor Fritz are the first American duo in the top 10 since Mardy Fish and John Isner in May 2012.

He has also won titles on every surface after claiming the Houston clay-court crown earlier in the year to add to his 2018 triumph on the hardcourts of Delray Beach.

"It shows that I'm a complete player. When I'm locked in I can play on every surface," Tiafoe said.