Rafa Nadal edged closer to a place in his first US Open final after thrashing Feliciano Lopez 6-3 6-4 6-4 with another devastating show of serving.
The world number one, who would complete the collection of grand slam titles with a victory at Flushing Meadows, wrapped up his fourth straight-sets win of this year's championships.
The start was delayed because of a backlog of matches and did not finish until early this morning, despite Nadal's best efforts to get it over as quickly as possible.
The result appeared a foregone conclusion after Nadal opened up a 3-0 lead in the first set.
"I am playing well, but not playing yet at my highest level," Nadal said.
Nadal has yet to lose a game on his service in the entire championship, and against Lopez, the 23rd seed, he won a staggering 90pc of first-serve points.
"I didn't play bad but he played better in (the) important points than me," Lopez said. "He doesn't give you so many chances in one match."
Nadal has worked hard on his serve in the belief it is key to his chances of finally conquering the New York surface. If his form over the past week is any guide, the wait may soon be over.
"To be in the quarter-finals of the US Open without losing a set and without losing a serve, two things must work really well: the concentration and the serve," Nadal said.
Nadal's opponent in tomorrow's quarter-final is another Davis Cup team mate, Fernando Verdasco, who advanced the hard way by wearing down David Ferrer 5-7 6-7 6-3 6-3 7-6.
Meanwhile, Kim Clijsters was relieved to emerge with a win but concerned she might not be so fortunate in her semi-final clash with Venus Williams.
"I didn't play a good match, but I was obviously able to win it," the defending champion said. "The next match everything will have to be a lot better," said Clijsters, who registered 43 unforced errors and lost her serve seven times during her 6-4 5-7 6-3 win over fifth-seeded Australian Samantha Stosur.