Leeds lost captain Liam Cooper to a hamstring injury in the warm up and former Whites target Oli McBurnie fired the dominant Swans into a 24th-minute lead.
Kemar Roofe then slammed home the equaliser five minutes before the break following excellent work from Cooper's replacement Jamie Shackleton on the right flank.
The excellent McBurnie then headed Swansea back into the lead six minutes after the interval but Leeds equalised for the second time with 11 minutes left when Hernandez produced a superb low finish after an excellent run and cross from substitute Patrick Bamford.
Leeds were dealt a major blow before the contest even started with captain Cooper pulling his hamstring in the warm up and replaced by Shackleton as Luke Ayling took the skipper's arm band and shifted to centre-back.
Swansea made the brighter start but without creating a plethora of chances with Martin Olsson blasting the best of them over the bar from the edge of the box in the 15th minute following a free-kick conceded by Kalvin Phillips for for a foul on Bersant Celina for which he was booked.
Leeds were then awarded a free-kick in a more central position shortly after but Barry Douglas saw his low effort easily held by Erwin Mulder.
Swansea were on top and Joe Rodon sent a header over the bar from a Celina corner before Connor Roberts blazed another effort over.
But the hosts were bossing matters and the Swans took the lead in the 24th minute when Leeds were carved apart after Phillips was dispossessed in the middle of the park.
Swansea raced forward through first Barrie McKay and then Celina who cut a pass back inside to McBurnie who rifled a low shot past Bailey Peacock-Farrell in the 26th minute.
Whites head coach Marcelo Bielsa quickly decided that a change was called for and took off Phillips for Lewis Baker.
But it was Swansea who squandered the next big chance when Jamie Shackleton lost the ball to Celina who flashed a powerful shot wide when he had McBurnie in support.
Leeds then missed a golden opportunity themselves when a Douglas cross after a cleared corner presented a free header for birthday boy Gaetano Berardi who sent his effort over the bar.
From another Swansea attack, the excellent Celina put a clever looped effort just wide but from nothing Leeds then levelled matters through Roofe after excellent play from Shackleton five minutes before the break.
The 18-year-old broke free down the right flank and fizzed over a powerful low cross which took out keeper Mulder, allowing Roofe to slam the ball into an empty net.
Gjanni Alioski was taken off for Manchester City loanee Jack Harrison during the half time break but Swansea were soon back on the back and the hosts regained the lead in the 50th minute.
Martin Olsson found space on the left flank and delivered an inviting cross which picked out McBurnie who had the space and time to produce a majestic looping header over Peacock-Farrell into the far right corner.
The Swans were well on top and McKay then blazed a fine effort just over the bar from the edge of the box before only a superb save from Peacock-Farrell denied McBurnie his hat-trick as the striker's low shot was tipped just wide just after the hour mark.
Already, Bielsa decided it was time to make his final change with Patrick Bamford brought on for Roofe and Bamford narrowly failed to latch on to an inviting cross from Baker in the 68th minute.
Leeds gradually got going and Samu Saiz looped another chance over from the edge of the box but the Whites were enjoying their best spell yet and made the most of it to level with 11 minutes left.
Bamford superbly broke free down the left flank and delivered a perfect cross for Hernandez to produce a clinical low finish against his former side.
The goal set up an end to end, grandstand finish and Swansea's Mike van der Hoorn put a header over the bar before Peacock-Farrell produced an outstanding save to deny Celina who was one on one.
Harrison then almost broke clear for Leeds and United went all out for the victory in four minutes of added time but had to settle for a highly entertaining draw.
Leeds United: Peacock-Farrell, Ayling, Douglas, Cooper, Berardi, Phillips (Baker 28), Klich, Alioski (Harrison 45), Hernandez, Saiz, Roofe (Bamford 64). Subs not used: Blackman, Shackleton, Shaughnessy, Pearce.
Swansea City: Mulder, Naughton, Van der Hoorn, Rodon, Olsson (Asoro 83), Fulton, Fer (Carroll 74), Celina, Roberts, McBurnie, McKay (Montero 64). Subs not used: Benda, James, Grimes, Dhanda.
Referee: Andy Davies.