The midfielder found his second goal of the game in the 88th minute to take all three points for the Stones, cancelling out Paul Hodges’ fine brace.
Slough began the match in fine fashion, with midfielder Hodges capitalising on a defensive mix-up before calmly chipping the ball over Ravan Constable with just three minutes on the clock.
But the lead was short-lived as Maidstone found a quick equaliser. Joan Luque’s deep free-kick found an unmarked Scott Rendell at the back post, and the forward made no mistake in guiding his header past Jack Turner and into the far corner.
The Rebels looked to respond almost immediately as great linkup play between Dan Roberts and Matt Lench allowed the latter an open opportunity, but his composed strike was tipped wide by Constable to deny the hosts.
And it was the away side who took a lead heading into the half-time interval. Gavin Hoyte made a darting run before finding Ibrahim Olutade in the box, the forward calmly laid the ball off for Porter to slot in on the 43rd minute.
The Stones started the second half looking to extend their lead, and they were almost successful when substitute Olutade forced a fine stop from Turner in the opening minutes of the half.
But it was the hosts who took control and levelled in the 55th minute. Max Worsfold’s searching pass found Dan Roberts on the left, and the forward timed his cross perfectly to find Hodges at the back post for an easy finish to make it 2-2.
Maidstone worked hard to maintain possession after the restart and Olutade almost made it 3-2 when he met George Elokobi’s low cross with a diving header, but Turner again saved the effort well.
Hodges nearly bagged his hat-trick after seeing his fierce strike inside the box fly just wide of Constable’s near post in the 70th minute.
But Maidstone continued to match Slough’s intensity and found a late winner through Porter’s second of the game. The attacker rose well before guiding his header past Turner in the 88th minute to seal a narrow victory for the Stones.
Report: Daniel Lewis
Maidstone United Lineup
Ravan Constable, Gavin Hoyte, Joe Ellul, George Elokobi, Noah Chesmain, Joan Luque (Ibby Akanbi 67), Sam Corne, Dominic Odusanya, George Porter, Scott Rendell (Ibrahim Olutade 38 (Charlie Seaman 86)), Justin Amaluzor. Unused substitutes: Chris Lewington, Kreshnic Krasniqi.