The big-hitting Spaniard holed out for a rare (three-under-par) albatross with a 9.5-degree driver at the 288-yard seventh on the hilly Lake Course at Olympic.
"This could sound a little ridiculous but it was an excellent shot," Quiros told reporters of his stunning blow while playing a practice round with compatriot Gonzalo Fernandez-Castano.
"I was playing a match against Gonzalo and I beat him thanks to this shot, so that's the most important thing," smiled the Spaniard, who retrieved his ball from the cup and then tossed it into the stands behind the seventh green.
"Unfortunately it was in a practice round but it is a good sign, isn't it? I finished the round with a good feeling and hopefully I can keep doing these things properly for the rest of the week."
Quiros, a six-times winner on the European Tour, is scheduled to tee off in Thursday's opening round in the company of fellow power hitter Gary Woodland of the United States and Australia's John Senden.
The 29-year-old Spaniard is competing in his fourth U.S. Open, having missed the cut in 2009 and 2010 before tying for 54th place at Congressional last year.