The Mexico striker scored the winner in Wednesday's Champions League quarter-final second leg victory over Atletico Madrid and scored twice on Sunday night in La Liga
The Mexico striker netted the crucial winner in Real's 1-0 defeat over Atletico Madrid in the second leg of their Champions League quarter-final tie on Wednesday and was decisive again on Sunday night.
Former Barca winger Nolito opened the scoring for Celta with a fine individual effort early on, though any celebrations in the Catalan capital will have been short-lived as Toni Kroos quickly equalised.
Hernandez, again playing in place of the injured Karim Benzema, put the visitors ahead, but their risky high defensive line allowed Santi Mina to score his fifth goal in three games before the half-hour mark.
James Rodriguez's deflected effort just before the break gave Real the lead once again, though the second half proved a serious assessment of their credentials, as the visiting defence withstood periods of intense pressure.
Nevertheless, Hernandez coolly stroked home the winner with 21 minutes to go, sparing Ancelotti's blushes once again as Madrid avoided a repeat of last season's crucial slip-up at Balaidos which ended their title hopes.
A repeat of that result had been on the cards as Celta's positive start was rewarded with just nine minutes played. Nolito brilliantly slalomed between Dani Carvajal and Asier Illarramendi before cutting in from the left flank and tucking a shot just inside the left-hand post.
But the visitors' reply was swift as they restored parity just seven minutes later.
Cristiano Ronaldo caused havoc in the Celta backline with a darting run into the right side of the area and Kroos was on hand to steer home in emphatic fashion from 12 yards despite Hugo Mallo's initial interception.
Hernandez completed the turnaround in the 24th minute, placing a cool finish under Sergio Alvarez after combining with Rodriguez down the right to devastating effect.
But Celta rallied and hit back within a few moments, as Mina raced beyond the Madrid defence and finished at the second attempt after hitting the post when running in on Iker Casillas' goal.
Ancelotti's side's chances of retaking the lead before the break seemed to end with Ronaldo striking the post in the 40th minute, but luck was on their side with their next attack when Rodriguez found the net from 20 yards via a deflection off Andreu Fontas.
Celta enjoyed victory at Barcelona in November and showed no sign of holding back. And their attacking endeavour could well have been rewarded with a penalty shortly before the hour mark when Kroos tripped Fabian Orellana in the box.
However, Madrid were happy to hit the hosts on the counter and Sergio Ramos' exquisite chipped pass released Hernandez to clinically beat Alvarez to cap a fine week individually and seal a result which keeps their hopes of winning La Liga alive.