Paul McCallum netted his second pre-season goal as Orient picked up a 2-1 win at the Chigwell Construction Stadium against National League side Dagenham & Redbridge.
Hessenthaler’s side fell behind when Oliver Hawkins netted from six yards, but Gnanduillet got on the end of a fine Dean Cox cross. and just as the game looked to be ending all square, Paul McCallum's stoppage time header saw Orient pick up the win.
The O’s included trialist Reece Brown in the starting line-up, while a number of those who were substitutes against Charlton Athletic at the weekend featured from the off, with Nigel Atangana starting with the captain’s armband.
Early chances came the way of the hosts as Fejiri Okenabirhie picked the ball up just outside the box and saw his curling effort deflected behind for a corner with Charlie Grainger at full stretch in the Orient goal.
Jordan Maguire Drew shot wide moments later, before the first meaningful O’s attack came after 12 minutes after Ollie Palmer managed to work an opening, but he dragged his effort wide of the far post.
Orient started to gain a foothold in the game and Dean Cox warmed the hands of home goalkeeper Mark Cousins from fully 25 yards.
But it was the hosts who went in front though on the 18 minute mark as the lively Okenabirhie delivered a pin-point ball in from the left and Oliver Hawkins was there at the back post to slot past Grainger.
They had a chance to double the lead 10 minutes later when the O’s lost possession in the box, allowing Christian Assombalonga time in the box, however, the striker blazed over from close range.
A chance came the way of Gnanduillet up the other end as he managed to get his head on the ball, only to see the effort easily saved by Cousins, before Cox fired over the bar from just outside the box.
Opportunities were few and far between as the game wore on, before Koroma almost levelled for the visitors in fine style. He controlled the ball nicely before volleying just wide of the post.
Hessenthaler’s side didn’t have to wait too much longer before equalising though as a lovely crossfield ball from Sammy Moore found Dean Cox out wide and he took one touch before crossing for Gnanduillet to finish on the volley from close range.
The O’s made three changes at the break, with Alex Cisak, Yvan Erichot and Sandro Semedo on for Charlie Grainger, Myles Judd and Josh Doherty making way.
The second period was slow to get going with neither side creating too much until an acrobatic effort from Gnanduillet after the hosts failed to clear a corner.
Up the other end, Cisak was forced into a good save at full stretch to deny Andre Boucaud before the game began to liven up.
Orient forced several corners in quick succession, with one coming as a result of a fierce deflected effort rom Sammy Moore, after Brown made Cousins make a strong save.
Some good skill from Freddy Moncur created another opening for the visitors as he played the ball back to Paul McCallum who could only see his shot deflected and the hosts saw off the danger.
A winner looked unlikely for either side until deep into stoppage time when McCallum's initial header from Sean Clohessy's cross was saved by Cousins, but the striker reacted quickly to nod the ball into the net.
The O’s will round off their pre-season campaign with a home encounter with League One side Gillingham on Saturday.
ORIENT: Grainger (Cisak 46), Judd (Erichot 46), Brown, Parkes (Clohessy 73), Doherty (Semedo 46), Koroma (Moncur 65), Atangana (Weir 61), Moore (Kelly 61), Cox (Massey 77), Palmer (McCallum 61), Gnanduillet (Bowery 73).