The younger Haas, who was the top qualifier at 5-under 135, defeated 64th seed Lee Williamson 1-up. Williamson, who took four shots to reach the 18th green, conceded Haas' putt on the final hole. Haas was within 10 feet in two shots.
'I guess it was good for me - him getting a bad break,' said Haas. 'That's not the way you want to win. I don't think I'm better than anyone out here because I'm the medalist.'
Haas became only the second medalist in five USGA amateur events to advance to the second round.
Dustin Bray, David Miller, Ricky Barnes and John Merrick, who were four of the five tied for second in stroke play, all advanced to the second round. Anthony Kim, who was in the upper bracket with Haas and the other player tied for second in qualifying, lost as Charlie Beljan scored a 1-up win. Beljan won the U.S. Junior Amateur earlier this year in Atlanta, GA.
Kevin Stadler was one of three players who qualified at 138 and is playing in his second U.S. Amateur. Stadler, son of PGA Tour pro Craig Stadler, and J.J. Jakovac each won their matches easily. Joe Affrunti, the other qualifier at 138, lost 3 & 2 to Derek Berg.
Of the players who tied for 10th place at 139 in qualifying, just two of the five moved on to the second round. Reid Hatley and Camilo Villegas each earned 1-up victories. Two of the other qualifiers at 139, Zach Atkinson and Chris Nallen, fell on the 19th hole to Brad Morris and Bruce McDonald, respectively. Julien Trudeau, the remaining qualifier at 139, lost to Dee Green 2 & 1.
Thursday will feature two rounds of match play, dwindling the field down to eight players. Haas will face Greg Kennedy, who also advanced with a 1-up victory over Fernando Mechereffe, in the first match. Merrick squares off against Hunter Mahan, while Miller faces Ryan Moore. Bray will take on Jerry Courville and Barnes will go against Daniel Summerhays.
Summerhays is the nephew of Senior PGA Tour player Bruce Summerhays. Stadler will battle Jason Powell.
Thursday's play will determine the quarterfinalists. The winners Friday will play in the semifinals on Saturday and the last two standing will meet in the 36-hole final on Sunday.
The 102nd U.S. Amateur champion, if he maintains his amateur status, will receive an invitation to next year's U.S. Open and has traditionally been invited to the Masters.