The American's consistent performance in challenging two-to-three foot conditions saw him secure a single-wave total of 7.17 - the highest of the day.
And that helped Dunphy on his way to a heat total of 13.84 and a place in the next round.
"I think the tide came up right when we were starting and the wind came up a little bit so it gave the wave a little crumble and a little extra time to fit in a couple of maneuvers," Dunphy said.
"I just wanted to go out and get a couple of waves where I could do two turns each. I hadn’t ridden this particular board since El Salvador and it feels really good and I think that helped me out as well."
Joining Dunphy in progressing was Gavin Gillette, another top seed, after the Hawaiian opened his campaign with victory.
"With Dylan (Goodale) and Brett (Barley), they’re both really good surfers in these conditions especially," Gillette said.
"I knew it was slow out there and there wasn’t much opportunity so anything that looked like it had a bit of a shoulder I was trying to go for and get a couple of scores and build a house. Luckily I did because in the end I didn’t get anything."
Round of 64 results:
Heat 1: Cristobal De Col (PER) 10.83, Michael Powell (USA) 9.37, Derek Peters (USA) 7.50, Keala Naihe (HAW) 6.36
Heat 2: Jeffrey Lukasik (USA) 9.00, Guillermo Satt (CHL) 6.37, Victor Done (USA) 5.70, Anthony Segura (CRI) 3.77
Heat 3: Tim Reyes (USA) 10.10, Colin Moran (USA) 6.66, Lucas Santamaria (ARG) 6.23, Makai McNamara (HAW) 6.40
Heat 4: Tanner Hendrickson (HAW) 11.83, Jeremy Johnston (USA) 9.20, Kevin Schultz (USA) 8.20, Oliver Kurtz (USA) 5.83
Heat 5: Gavin Gillette (HAW) 11.84, Dylan Goodale (HAW) 7.64, Brett Barley (USA) 7.34, Adrian Rodriguez (MEX) 4.94
Heat 6: Phillip Goold (USA) 9.00, Camilo Hernandez (CHL) 8.54, Dylan Southworth (MEX) 7.70, Michael Valasco (USA) 4.64
Heat 7: Diego Cadena (MEX) 10.53, Dane Anderson (USA) 9.00, Evan Thompson (USA) 7.20, Angelo Lozano (MEX) 6.76
Heat 8: Jose Trujillo (MEX) 9.97, Blas Bacardo (MEX) 5.94, Nic Hdez (USA) 5.66, Liam McNamara (HAW)
Heat 9: Michael Dunphy (USA) 13.84, Jean Schaffer (VEN) 8.73, Koa Rothman (HAW) 5.40, Morgan Faulkner (HAW) 4.50
Heat 10: Rafael Pereira (VEN) 10.74, Cory Arrambide (USA) 10.17, Balaram Stack (USA) 7.27, Landon McNamara (HAW) 3.10
Heat 11: Alan Saulo (BRA) 11.50, Manuel Selman (CHL) 8.84, Johnny Norris (USA) 7.40, Nathan Carvalho (HAW) 7.30
Heat 12: Carlos Munoz (CRI) 9.70, Taylor Clark (USA) 8.50, Fisher Heverly (USA) 8.03, Colt Ward (USA) 3.67