The result means the Lions remain in the relegation places and have yet to win away from home this season.
Speaking after the loss, Cox said: “It was a very disappointing loss, to concede twice so early left us a lot of work to do and built their confidence. We just have to now focus on our Tuesday game against Macclesfield.”
Guiseley announced the signing of former Leeds United youngster Simon Lenighan, who started on the bench and came on before the break.
Guiseley made a terrible start, conceding twice in the opening five minutes. Goalkeeper Joe Green spilled a header and Ryan Upward tapped in before Harry Pritchard fired a stunning shot into the top corner.
Guiseley almost got back into the match when Lee Molyneux’s cross was headed towards goal by Jake Lawlor but Jake Goodman headed it away.
The visitors kept pressing but Maidenhead were able to get a third goal before half-time when James Comley outpaced the Guiseley defence and chipped Green.
It could have been even worse for Guiseley just before the break when Adrian Clifton hit the post.
The pace at the start of the second-half slowed, but again it was the hosts who created the half-chances.
Guiseley tried to get back into it with Lenighan firing wide and Reece Thompson unable to get his shot on target from a tight angle.
Maidenhead United: Pentney, Clerima, Steer, Odametey, Massey, Comley (Smith 72) Barrett, Pritchard (Kilman 80) Clifton, Upward (Inman 86) Goodman. Unused substitutes: Peters, Hyde
Guiseley starting 11: Green, Lowe (Lenighan 43) Palmer, Atkinson, East, Molyneux (Wesolowski 45) Lawlor Rooney, Hatfield, Thompson, Odejayi (Mulhern 70). Unused substitutes: Maxted, Hurst.
Referee: S Allison.