United youth product Gomes, 18, struck after Spurs’ Lucas Moura cancelled out Anthony Martial’s first-half opener and gave the 20-time Premier League champions another victory after they beat Perth Glory, Leeds United and Inter Milan.
However, United manager Ole Gunnar Solskjaer’s joy was tempered by a knee injury to central defender Eric Bailly, who was carried off 10 minutes after his halftime introduction.
United had the better of the opening exchanges against last season’s Champions League runners-up, with Martial hitting the post after four minutes, although Spurs midfielder Dele Alli then forced David De Gea to turn a low shot around the post.
United kept Tottenham’s defence under pressure, however, and Brazilian Andreas Pereira slid the ball to Martial who took advantage of goalkeeper Paulo Gazzaniga’s poor positioning to slip the ball home at the near post after 21 minutes.
New United signing Daniel James threatened with his pace and Paul Pogba went close with a long-range effort as the Old Trafford side ended the first period in the ascendancy.
Solsjkaer changed his entire lineup for the second half with Spurs manager Mauricio Pochettino switching six players.
The Londoners equalised in the 65th minute when Moura’s shot from the edge of the area took a deflection off Luke Shaw that wrong-footed substitute goalkeeper Sergio Romero.
But Gomes had the final word when the jet-heeled winger burst into the box to pick up a return pass from Juan Mata before slotting a shot across Gazzaniga into the bottom corner.
