Andy Roddick fired the fastest serve of all time in his quarter-final win over Paradorn Srichaphan at Queen's.
Roddick broke his own world record by 1mph as he produced an unreturnable bullet of 153mph.
"I didn't try and hit it any harder than normal - I didn't realise anything until the crowd started cheering," said Roddick of his record-breaking serve.
The new record will not be made official until the speed has been checked and verified.
Top seed and world number two Roddick had the edge throughout the match and a single break of serve midway through gave him the first set.
He broke twice more in the second set for a 6-3 6-3 victory that sets up a semi-final with Lleyton Hewitt.