The rising 20-year-old from Irvine said it "meant a lot" for him to him to beat fellow American lefty Ben Shelton 7-6 (3), 4-6, 6-3 on a sun-soaked Stadium One court to advance under sunny skies in the California desert.
"The court I played on today, I remember exactly where I was sitting in that same stadium when I was a kid, so it's really cool, it's a full-circle moment for me," he said.
"From where I was sitting on the bench, it was to my left, in the corner. I remember those seats. I remember a lot of it still."
He said he was fortunate to grow up in Southern California, a region with deep roots in the sport that offers ideal weather for year-round practice and competition.
"There's a lot of tennis, a lot of tennis courts, a lot of tennis players, and a lot of parents putting their kids into tennis programs," he said.
"There were a lot of tournaments around. I wouldn't have to travel that far most of the time, and it wasn't that hard to find open courts. I consider myself pretty lucky to have grown up in this area."
Tien, seeded 25th, admitted to feeling some nerves in his match against world number eight Shelton, who despite suffering from an illness still presented a formidable challenge with his world-class serve and powerful groundstrokes.
"Tricky match, for sure. Going out there, I heard that maybe he wasn't feeling that great. So it wasn't super surprising to me that he was just taking big cuts, he was going for a lot of balls. Just overall a tough match to navigate.
"I think I played the match without having a whole lot of rhythm, just because of how big he was playing. I also felt a little bit of the nerves in some of those points. But just happy to get through."
With the win over Shelton, Tien is now 6-5 in his career against top-10 players and next faces Spain's 19th-ranked Alejandro Davidovich Fokina.