Van de Zandschulp was initially set to face Tallon Griekspoor in the first round, but instead faced Aleksander Shevchenko after Griekspoor's withdrawal. Van de Zandschulp's straight-sets win left him the sole Dutchman in the Cincinnati main draw, with Jesper de Jong knocked out in straight sets by Alex Michelsen.
Van de Zandschulp faced 26th-ranked Fonseca next, who opened his tournament on Sunday after a first-round bye.
It was a flying start for Van de Zandschulp, who had a break chance in Fonseca's first service game and broke the Brazilian in the next to make an early mark in Cincinnati. However, the Dutchman faced an immediate re-break that seemed to awaken Fonseca.
The Brazilian overpowered Van de Zandschulp with a love game to take full control of the momentum, though the Dutch underdog stayed in the fight. A poor service game late in the first set cost him dearly, however, with Fonseca profiting from Van de Zandschulp's mistake to take the first set after 41 minutes.
Fonseca had no trouble discarding Van de Zandschulp in his service games and dealt the first break himself this time around, putting the Dutchman down 3-1 to open a lane towards another match win.
Late comeback?
With two break chances in hand, Van de Zandschulp hit two unforced errors to keep Fonseca firmly in the driver's seat. The Dutchman saved a break point at 4-1 to stay alive and forced his way back into the game with a re-break to make it a one-game deficit at 4-3.
The revived Van de Zandschulp had Fonseca facing a 30-0 deficit at 4-4 when the Brazilian got a time violation after losing 12 of the previous 15 points and got a break chance at 40-30 to really turn the set around, but lost with a wayward return on Fonseca's strong kick serve. It wasn't to be for Van de Zandschulp, who saw Fonseca hold his service game and get within one game of the win.
Van de Zandschulp lost his rhythm in his following service game, giving Fonseca the lead through a double fault, but survived nonetheless. Fonseca secured his spot in a tiebreak with a love game - a favour Van de Zandschulp returned to force a crucial second-set decider.
Fonseca started the tiebreak on the front foot with a quick mini-break and completely took over from there, profiting from several errors from Van de Zandschulp to end the tiebreak at 7-2 and book a ticket to the third round.
With his win on Sunday, Fonseca will face Australian qualifier Christopher O'Connell next. O'Connell progressed to the third round after Casper Ruud's retirement.