Ajax have missed out on the chance to extend their two-point advantage at the top of the Eredivisie table as they slipped to a 1-0 reverse away to FC Urecht.
Ajax had a first-half chance through Arkadiusz Milik but the Polish striker's effort was well blocked by the home side's defence.
Utrecht were appealing for a penalty after the hour mark when the ball appeared to hit Jairo Riedewald on the arm, but the official waved away the shouts.
With the game heading towards a goalless draw, Yassine Ayoub struck with three minutes of normal time remaining to move the home side up to sixth in the Dutch league.
