Ex-Elland Road academy player Oliver McBurney had looked like upsetting his old club with two goals either side of Kemar Roofe's fourth of the campaign.
However, Hernandez swept home 10 minutes from time and, although Leeds lost the SkyBet Championship's only remaining 100 per cent record, a point was enough to take them top of the table on goal difference from Middlesbrough.
The draw also lifted Swansea, still unbeaten themselves, into third place.
At the other end of the table QPR extended their unwanted 100 per cent record with a fourth successive defeat after losing 3-0 at home to Bristol City.
Andreas Weimann struck twice after Matty Taylor had opened the scoring just before half-time as Steve McLaren's side's defensive woes continued, with 13 now conceded in four matches.
After back-to-back league defeats Derby returned to winning ways with a 2-0 victory over Ipswich.
Joe Ledley's 25-yard strike on the hour broke the deadlock and Tom Lawrence's free-kick from similar distance gave Frank Lampard his second win as a Championship manager.
Hull came from behind to win 3-2 and end Rotherham's best home run since April 2001.
Richard Wood's early header put the hosts ahead, but Australia international Jackson Irvine equalised on the counter-attack and, after Fraizer Campbell struck on the stroke of half-time, Irvine added his second just after the break.
Jamie Proctor pulled one back with 15 minutes remaining, but the hosts could not force an equaliser.