Slough handed Kyle Anthony his first start after the departure of Nathan Bowden-Haase, and he had a steady debut alongside Alex Brown at the heart of the defence.
The hosts had started as the more threatening side, and forced stand-in goalkeeper Jamie Jackson into two good saves early on, through Dan Moody and Will Heavey.
Dan Burnell gave Slough a 19th-minute lead from the penalty spot after the referee had spotted a foul on him as Ashley Deeney cut the ball back from the right.
But Guildford levelled nine minutes before the interval through Heavey, who headed a cross from Junior Kaffo across Jackson and into the corner of the net.
Scott Elgar’s cross clipped the bar as Jackson was nearly caught out, but Slough were by far the more threatening side in the second half and Burnell twice had shots saved by keeper Antony Hall as the Rebels were frustrated - one good low stop, later followed by a flying save to turn away a shot which looked bound for the top corner. Slough, though, were unable to find a way through to goal and were denied by the offside flag on a number of occasions.
Ed Smith was also denied after a knock-down from Adam Martin, as Steve Bateman's side had to settle for a point on their long-awaited return to action at a cold Spectrum ground.
Guildford City Line up
Antony Hall, Elvis Defreitas, Ben Rayner (c), Tom Penson, Jamie Thoroughgood, Scott Elgar, Dan Moody, Will Heavey (Luke Bradnick), Junior Kaffo (Casey McCabe), Scott Todd (Bruce McPhail), Dammy Bada. Subs not used: Tony Chaplin, Mike Hall.