Alexander Zverev had "no answers" as he lamented a dismal display in his US Open loss to Taylor Fritz. (More Tennis News)
Fritz downed Zverev 7-6 (7-2) 3-6 6-4 7-6 (7-3) in the last eight on Wednesday.
In the process, Fritz reached his maiden grand slam semi-final, and will face fellow American Frances Tiafoe for a place in the showpiece match at Flushing Meadows.
World number four Zverev, meanwhile, had to lick his wounds after what he labelled a "terrible" performance.
“I played terrible," said Zverev.
"I just have no answers right now. He played quite a good match. I did nothing to deserve to win."
Matters could have not been more different for 12th seed Fritz, however.
"I feel amazing," he said. "I've had a lot of looks at quarter-finals in the past couple of years, and today just felt different.
"I really feel that it was my time to take a step further and it;s only fitting I'm doing it here on this court at the [US] Open in front of this crowd.
"Today just felt different. I really felt like it was my time to go a step further. It's only fitting I'm doing it here on this court, at the Open, in front of this crowd."
With Tiafoe also progressing to the last four, it will be the first time two Americans have played each other in the US Open semi-finals since 2005.
The last time an American man reached the final at Flushing Meadows was in 2006, when Andy Roddick lost to Roger Federer in 2006.
