He had signed from Canterbury City on the morning of the match and went on to produce a string of excellent saves to prevent the Rustics from winning the game comfortably.
The home side started strongly despite lacking the injured Reuel Powell-Downey, and pushed the visitors back from the first whistle.
Rusthall’s slick passing game was causing Kennington problems and Mant showed his class when turning a vicious strike from inside the area wide of the left-hand post.
From the resulting corner Rusthall went close again, but Steve Camacho’s shot was blocked by a defender on the line.
Rusthall’s midfield, marshalled by skipper Paul Butler, was dealing comfortably with everything the visitors tried.
But despite the Rustics’ dominance it took until the 27th minute for them to break the deadlock.
A corner from the right by Lawrence found leading scorer Luke Adams beyond the far post and the in-form striker expertly beat his marker and unleashed a right-foot shot that gave Mant no chance.
Kennington looked more positive after the break but struggled to test the home defence with young centre-backs Ryan Styles and Robbie Bissett keeping them at bay.
The Rustics continued with their slick passing game and they came close to securing victory when a good build-up down the right found Louis Anderson on 73 minutes.
His cross was headed down to Adams, who met it first time and his shot looked to be flying into the top right hand-corner only for Mant to produce an exceptional full-length save to tip it around the post.
This seemed to give the visitors a lift and they threw bodies forward in an attempt to get something from the game.
But Rusthall showed what a good side they have become in the 12 months since Jimmy Anderson took over as manager, closing the game out well.
The victory moves them up to second in the Southern Counties East League Division One, three points behind leaders Rochester United with four games in hand and level with Holmesdale in third place.
The Rustics now face a testing away game against fourth-placed FC Elmstead on Saturday (December 21, kick-off 3pm).
