Cheng Tsung Pan of Taipei beat Jay Moseley 2 and 1 and George Zahringer sunk a four-footer on the 18th hole to beat England's Gary Wolstenholme, 1-up.
Those two will join the 30 other winners Thursday for two separate rounds of match play. That will leave just eight players by Friday, four on Saturday and two in the 36-hole final Sunday.
'I'm really surprised,' said Pan, who had tried to qualify for the U.S. Amateur once before in San Diego but fell short. 'I didn't think I would qualify, but I did.'
Pan showed a deft touch around the greens, with a crucial chip on the 16th hole that landed within six inches.
Moseley holed out from a bunker on the second hole, but Pan never trailed. He took the lead for good on the 12th after Moseley sliced his drive and hit a tree.
The 54-year-old Zahringer took advantage of a drop on the 18th hole to advance. A valve cover offered him relief, and his drop lie was not only better than the original lie, but it also gave him a slightly better angle to the green. He eventually converted a four-footer to close out Wolstenholme, the third-oldest golfer in the field at 47.
'We made some uncharacteristic mental errors out there,' he said. 'I had trouble with the pace of the greens.'
Due to a fog delay Monday, the final 64-man match play field wasn't set until early Wednesday morning, when the 315 entrants were finally done with 36 holes of stroke play.
There were 17 tied at 7-over par for six spots, and they played four extra holes to determine the final qualifiers.
Although Alex Prugh was 2-under in stroke play, he lost on the 19th hole to Jon Curran.
Stroke-play medalist Jason Kokrak, 3-under in the stroke play portion, beat A.J. Oleksak 2 and 1.
'I was trying to play aggressive today,' said Kokrak. 'But overall I tried to stick to my game plan of hitting 3-irons and 3-woods off the tee.'
As for his putting?
'Phenomenal,' Kokrak said. 'I'm putting real well this week.'