Slough's poor recent run looked like continuing as the Rebels went 2-0 down in the opening 17 minutes.
First, Chris Bacon volleyed in past debutant keeper Aleksandar Gogic on 10 minutes, the Lilywhites striker finishing off good build up play with a shot that flew into the top corner.
Seven minutes later, Josh Dawkin scored with an inch perfect finish from 25 yards out, after running at the Slough defence. He collected the ball just inside the Rebels’ half, and Slough backed off him, allowing him to score a great goal which lifted the home crowd.
City could well have killed the game off when Chris Bacon had a great chance to make it 3-0, but his effort was blocked by Gogic. The home side were impressing all over the park, with Slough looking overrun.
But Reece Yorke pulled one back for Slough as he headed in James Dobson's cross. Keeper Harry Reynolds came out to try and claim the ball, but the ball missed his outstretched arm and Yorke made no mistake to head the ball into an empty net.
Slough were back in the game, but Dawkin struck again two minutes before half time to restore City's two-goal lead as the hosts continued to play at a high tempo. The goal came after more good build up play and excellent skill from the impressive Michael King to find Dawkin, and he fired into the bottom corner.
City started the second half well, and Bacon could have scored his third but was unlucky to see his header off target after meeting an excellent cross from Charlie Day. Sadly for Bacon, he picked up an injury and needed to leave the field shortly after, replaced by Neil Midgley.
Slough went on to have much the better of the second half, and Scott Harris brought Slough back to within one goal on 53 minutes, as he reacted quickly in the six yard box to slot the ball home past Reynolds.
Substitute Jake Parsons fired a low shot across the area with 10 minutes left which was well held by Reynolds, and time looked to be running out for Slough, despite their best efforts. But with three minutes remaining, Smith completed the comeback.
Reynolds attempted to claim a corner under pressure, but dropped the ball and, after an initial shot bounced off the bar, the ball fell invitingly for Smith to smash it into an empty net amidst a goalmouth scramble.
Cambridge City Line up
Harry Reynolds, Ieuan Lewis, Charlie Day, Adam Martin, Lee Chaffey (c), Buster Harradine (Oliver Emsden), Michael King, Heidar Juliusson, Danny Kelly, Chris Bacon (Neil Midgley), Josh Dawkin. Subs not used: none.