Grays looked to take charge of the game from the very start and looked mostly likely to take the lead.
In only the 3rd minute Grays pressed forward before a volley from the edge of the area by Luke Marshall went inches passed the left hand post.
Shortly after, good closing down allowed the ball to run to Joe Sweeney on the edge of the area. His turn and shot looked goal bound but went inches passed the post.
Grays again looked threatening in the 7th minute as Leon Lalite fired towards goal from the corner of the area. The shot was parried by Joe Wright in the Maldon goal, but before Jack West could react to the rebound, the assistant flagged for offside.
In the 9th minute Joe Sweeney had another opportunity to give Grays the lead as he picked up the ball on the edge of the area but his curling shot went inches over the bar.
Maldon had to wait until the 29th minute to have their first shot at goal as John Glowacki weaved his way into the area before firing narrowly wide at the near post.
The final chance of the half fell to Grays as Danny Bunce stormed down the left wind before crossing into the area. The ball found Jack West at the back of the area but his shot curled narrowly over the crossbar.
Grays continued to press at the start of the second half, forcing three corners in quick succession.
In the 57th minute Daniel Subuola was replaced with Joao Carlos.
On the hour mark Joe Sweeney was fouled on the edge of the Maldon area. Danny Bunce fired the ball toward goal but the ball hit the arm of Michael Toner and the referee awarded a penalty.
Danny Bunce stepped up to fire the ball low into the right hand corner, sending Joe Wright the wrong way.
Maldon had to wait until the 75th minute for the second real effort on goal, and some effort it was. John Glowacki picked up the ball thirty yards out, move towards goal and fired into the top right hand corner for twenty five yards, leaving George Kamurasi with no chance.
The home side almost took the lead just two minutes later as a free kick from Jamie Guy from the edge of the area was on target before George Kamurasi pushed the ball over the bar.
Despite Grays dominance throughout the game, they were hanging on for the last five minutes as Maldon began to show signs of why they have been so impressive this season.
In the 84th minute, Jamie Guy was played through on goal, but with the whole goal to aim at, fired narrowly passed the left hand post.
As the referee blew for full time, both teams were left with the prospect of a penalty shoot-out.
Danny Bunce stepped up first and this time fired the ball into the top right hand corner to give Grays the lead.
John Glowacki took the first Maldon penalty, firing low to left and George Kamurasi guessed correctly to push the ball away to give the away side an early advantage.
Leon Lalite took Grays second penalty looking to cement the advantage but his low shot to the left was saved by Joe Wright to give the home side hope.
Maldon levelled the score at 1-1 by scoring their second penalty.
Joao Carlos, Jared Small and Joe Sweeney all stepped up and scored their penalties, which Maldon in return answered with a successful strike of their own.
Luke Marshall made the walk from the half way line to the penalty spot with the score at 4-4 and coolly fired into the bottom left hand corner to once again put the pressure on Maldon.
Lewis Dark took the 12th penalty of the shoot-out, low to the left hand side, which George Kamurasi guessed correctly to increase his ever increasing reputation by saving the decisive penalty.
Grays continue on the Quarter Final and face an away tie at barking.
Grays Athletic: George Kamurasi, Lee Flynn, Junior Baker, Dave East, Danny Bunce, Luke Marshall, Kenny Beaney, Leon Lalite, Daniel Subuola (Joao Carlos 57), Jack West (Jared Small 69), Joe Sweeney
Unused Subs: Ryan Kirby, George Smith, Tyrone Scarlett