Gilles Muller of Luxembourg caused a huge upset by defeating Andy Roddick in the first round of the US Open at Flushing Meadows on Tuesday.
Roddick, who won the title in 2003, went into the featured night-session match as an overwhelming favourite.
But former world junior champion Muller had the measure of the American, dominating the big-serving encounter to win 7-6 (7-4) 7-6 (10-8) 7-6 (7-1).
Muller will play Robby Ginepri or Guillermo Garcia-Lopez next.
Former US Open champion Roddick admitted he was in shock after crashing out at Flushing Meadows on his 23rd birthday.
"I don't really remember a loss where I've felt this bad afterwards," said Roddick after his defeat.
"I've never felt better going into a (grand) slam than I did here. This has totally blindsided me. I felt like I was going to have a pretty good run.
"I love playing here. I probably had the best practice week I've ever had."
Muller, who was playing at Flushing Meadows for the first time, believes his relaxed approach to his encounter with Roddick was the key to his win.
"I have no idea (how I did it)," Muller said afterwards of the victory on his U.S. Open debut.
"For me it was just unbelievable to come out here. I told myself to just enjoy it and I did it every minute."