The live TV game went the way of the hosts as a strike from full back Marvin Ekpiteta on 72 minutes was enough to split an evenly contested clash in the east end of London.
The early start didn't stop over 900 Wrexham fans turning up at Brisbane Road to support the boys, but with International Clearance not arriving for new loan signing Jermaine McGlashan he had to join them watching on from the sidelines.
First chance of the afternoon came after just two minutes, when an Orient corner fell to Craig Clay just inside the Wrexham box and his effort pass only inches outside of Rob Lainton's right hand post.
Moments later and Brad Walker needed attention before limping to the sidelines, only to be replaced by Grant.
Ben Tollitt set off on one of his jinking runs and was promptly hacked down by right back Marvin Ekpiteta, who was booked for his troubles on eight minutes.
Midway through the first half, and Tollitt took a ball over the top, turned inside Ekpiteta, before firing across goal and only just pass
Moments later and Stuart Beavon almost got the better of Jamie Turley, but with the centre-half going to ground the referee blew up for a foul, the Orient man can count himself lucky on this occasion.
Another couple of minutes on and Jay Simson pulled the ball back for ex-Wrexham forward Jordan Maguire-Drew, who had the space and time to hit a shot, but from the edge of the box he fired over Lainton's cross bar.
A Luke Young free kick on 28 minutes was whipped in to the Orient box, where Grant was waiting but, in the end, it was put behind for corner.
That flag kick ended with another cross, which either Akil Wright or Jake Lawlor might have got a head too, but in the end a fine defensive header cleared the danger.
Beavon and Turey were having their own private battle, as the two veterans were not giving an inch to each other.
More Wrexham pressure in midfield saw Paul Rutherford win the ball back, although his curling cross field pass looking for Grant, curled just a few feet too much and allowed keeper Dean Brill to race out and collect.
Wrexham were not holding back in the closing minutes of the half, forcing successive corners and the O's were just glad to clear their lines.
Grant was happy to have a shot at goal when the opportunity arose, keeping the home defenders on their toes.
Not that Leyton Orient were sitting back and on 43 minutes, a cross from Sam Ling on the right wing, found the head of Macauley Bonne in the six-yard box, but he flashed his header wide from a promising position.
Five minutes after the restart, a long ball out wide found Ling on the Orient right, he cut inside but Lainton was quickly off his line to meet him and block the shot, before the two came together and the game had to be stopped for them to receive treatment.
Shortly after, Wrexham pressure from a throw in, saw Rutherford have two crosses in from the right, second of which was knocked down by Wright for Tollitt and his shot needed to be kicked away to deny the winger.
On the hour, the home side made their first change with James Brophy replacing Ling.
James Jennings was shown a yellow card on 63 minutes for clipping the heels of Joe Widdowson, after the midfielder had overlapped down their right.
Maguire-Drew was at the heart of most thongs that Orient did, with a free role behind his forwards, indeed, he was not far frm getting on the end of Widdowson cross that was in turn flicked on after
On 70 minutes, Beavon made way for Jason Oswell.
Just two minutes later and Orient took the lead when Wrexham failed to clear their lines, and they had several chances to do so.
The ball sat up nicely for Ekpiteta to have a shot that might well have taken a slight deflection and just managed to beat Laintion, coming off his left-hand post.
A high cross in from Kennedy looked an easy take for Brill, but he didn’t catch it high allowed Grant to get a touch to dislodge it. The keeper was spared any blushes as he was able to collect at the second attempt.
There was a late appearance for Cole Stockton, as off came Tollitt with eight minutes remaining.
Wrexham pushed bodies forward in the final stages, looking for a way back into the game.
Into added time and Stockton unleashed a stinging effort, but Brill was right behind it to punch away - a couple of yards either side and it might have been so different.
There were to be no late heroics this week though, as the O's held out to take the points and dislodge the Dragons from top spot.
Leyton Orient: Brill, Ling (Brophy 58), Widdowson, McAnuff, Clay, Bonne, Maguire-Drew (Coulson 88), Happe, Ekpiteta, Turley, Simpson (Harrold 84).
Subs: Sargeant, Gorman.
Wrexham: Lainton, Kennedy, Pearson, Lawlor, Jennings, Walker (Grant 6), Young, Wright, Rutherford, Beavon (Oswell 70), Tollitt (Stockton 82).
Subs: Dibble, Roberts.
Referee: James Oldham (Derbyshire)
Leyton Orient: Ekpiteta (8, foul), Happe (90+4, time wasting)
Wrexham: Jennings (63, foul)