Two goals from Gelhardt together with strikes from Max Dean and Charlie Allen had Leeds heading joint top of Premier League Two Division One
But Amari Miller was then sent off for a second yellow card after a melee and Rovers drew level deep in added time as part of a Friday night epic.
Suspended first team defender Pascal Struijk once again lined up for Leeds who made a slow start and keeper Kristoffer Klaesson produced a good save to deny Sam Burns who got through down the right in the ninth minute.
Leeds United ‘would have taken’ four points from two games according to Alan Shearer
Leeds United ‘have not’ approached pair but in transfer ‘talks’
Leeds United U21 2-2 Norwich City U21 highlights: Joseph and Perkins score again
Leeds United's new predicted Premier League finish after double boost with new lows for rivals
Leeds United transfer news: former Leeds target ‘agrees’ £38m Wolves move, Man Utd ‘weighing up’ move fore Leicester City forward
United's first attempt on goal did not arrive until the 18th minute when Sam Greenwood's curled attempt from distance was saved.
But the Whites went ahead five minutes later as Gelhardt struck his fifth goal of the season to finish a rapid counter attack that started with a fantastic block by centre back Kris Moore.
The Whites worked the ball to Cody Drameh and then Gelhardt on the right flank and the striker cut inside and beat two men before unleashing a fierce left-footed drive into the bottom left corner.
A Dean flick was then cleared off the line four minutes later but Rovers equalised in the 28th minute as a long punt by keeper Jordan Eastham played in Burns who was able to poke the ball past Klaesson.
Matters then got worse for Leeds six minutes later when the lively Burns bagged his second of the game.
Leeds looked to break but former Whites midfielder Bradley Johnson produced a terrific challenge on Greenwood and United were cut open through the middle of the park.
Rovers then worked the ball to Burns who produced a cheeky finish through the legs of Drameh that rolled past Klaesson into the bottom right corner.
Leeds almost drew level seven minutes before the break when Gelhardt let fly from 20 yards out with a low drive that Eastham tipped wide.
But Gelhardt proved instrumental in Leeds equalising in the following minute by producing a beautiful through ball for Miller whose square ball across the box left Dean with a tap in.
A Greenwood free-kick from the edge of the box then flew wide before Dean fired over as Leeds ended the half well on top.
Struijk and Drameh were taken off at the break as Leo Hjelde and Liam McCarron were introduced.
Hjelde produced a superb block to keep out a Connor McBride shot from close range four minutes after the restart and within 60 seconds Leeds were ahead after Gelhardt robbed Johnson of possession on the edge of the Rovers box and thumped home a low finish for his sixth of the campaign.
Gelhardt was then substituted to a huge applause as Stuart McKinstry was brought on.
Just three minutes later, United bagged their fourth goal of the game as Allen headed home a Greenwood cross to finish a fine move that started with a Klaesson pass down the left for Miller.
Allen almost struck again two minutes later when firing just wide before a Greenwood shot was deflected over.
Dean's header from a corner was also blocked but Rovers pulled a goal back in the 67th minute as Jared Harlock produced a beautiful finish into the top left corner from the edge of the box.
Blackburn then pressed for an equaliser and Harlock put a free header wide.
With five minutes left, Lenny Cirino's reaction to a challenge sparked a melee after which four players were booked, including United's Miller who had already been cautioned and was sent off.
Blackburn then went all out for a late equaliser and Klaesson produced two strong saves as Leeds headed for six minutes of added time.
Leeds looked to be heading for victory but Rovers drew level in the 96th minute as Klaesson spilled Sam Durrant's free-kick that was then prodded home from close range by Luke Brennan.
Even then the drama was still not done as Klaesson was caught by a challenge but after 100 minutes of football an eight-goal thriller was finally brought to a close.
Leeds United under-23s v Blackburn Rovers under-23s: Klaesson, Drameh (Hjelde 46), Struijk (McCarron 46), Bate, Moore, Kenneh, Dean, Greenwood, Gelhardt (McKinstry 57), Allen, Miller. Subs not used: Van Den Heuvel, McGurk.
A message from the Editor:
Leeds has a fantastic story to tell - and the Yorkshire Evening Post has been rooted firmly at the heart of telling the stories of our city since 1890.
We believe in ourselves and hope you believe in us too. We need your support to help ensure we can continue to be at the heart of life in Leeds.
Subscribe to our website and enjoy unlimited access to local news and information online and on our app.
With a digital subscription, you can read more than 5 articles, see fewer ads, enjoy faster load times, and get access to exclusive newsletters and content.
Click here to subscribe.
For more details on our newspaper subscription offers click here.
Thank you Laura Collins