EUGENE (AP) - Tyson Gay got quite a fright in his first race Saturday. He set a record in his second.

Gay broke Maurice Greene’s American mark in the 100 meters by running 9.77 seconds in his quarterfinal at the U.S. Olympic track and field trials.

“It tells me I’m in pretty good shape,’’ Gay said. “We’ve got two more rounds left.’’

Gay tied the fourth-fastest time in the history of the men’s dash, despite clearly easing up a tad over his final few strides. Still, that was nothing compared what he did in his opening heat earlier in the day, when Gay came awfully close to a monumental blunder.

After building a big lead, the reigning world champion eased up a lot with about 30 meters left — so much that the rest of the field began to catch him. Gay was forced to accelerate again and he lunged across the finish line in fourth place, good enough to advance.

“The first round I was scared. I almost started crying. I didn’t know if I made it,’’ Gay said after bettering the record Greene set in 1999. “This round I felt good.’’

As well he should. The performance had to be a big boost of confidence for Gay, who was a distant second — a spectator, really — in New York on May 31, when Jamaica’s Usain Bolt broke the world record by clocking 9.72.

Gay’s had to answer plenty of questions about how much of a challenge he’ll present at the Beijing Olympics to Bolt and another Jamaican, previous world record-holder Asafa Powell.

Could Gay challenge Bolt’s mark in today’s semifinal or final?

“Anything’s possible,’’ said Wallace Spearmon, who sneaked into the semifinals by running 10.07. “Tyson’s fast.’’

So is the track at Hayward Field, which already has produced two U.S. records in running events and is serving up the sort of dry, hot weather — the temperature hit 95 degrees Saturday — conducive to quick sprinting.