Although United rarely looked like breaking their sequence of three successive goalless draws in Spain, Sir Alex Ferguson will not care too much about that.
The mere fact Hernandez's goal, drilled expertly into the far corner after fellow substitute Federico Macheda had cut a cross back from the right, proved United with only their second victory in 19 attempts against Spanish opposition in Spanish soil tells you just how hard it is.
Instead of having ground to make up in the battle to reach the knock-out phase, United can now look forward to back-to-back clashes with Group C makeweights Bursaspor knowing six points will virtually secure their place in the last 16 of this season's Champions League.
Having called for greater defensive solidity, the return of Rio Ferdinand ensured Ferguson got it and now United will hope to take that form into their Premier League challenge as well following recent hiccups.
Ferguson only needed to look at the record books to understand how hard it would be to win.
On 18 trips to Spain to face Spanish opposition, the solitary victory came against Deportivo La Coruna in 2002.
United's last three visits had ended goalless, which would probably have been an acceptable outcome from what on paper at least is their hardest Group C fixture, even taking into account that surprising stalemate with Rangers at Old Trafford a fortnight ago.
It seemed Valencia would not be too displeased either given the cautious manner with which they attempted to find a way through a side for whom Dimitar Berbatov was expecting forward support from Anderson.
Berbatov last started a match in this competition in Moscow 11 months ago. It was 12 months prior to that since his last goal.
He came close to ending the drought when he cut inside from the left touchline where he spent so much time and curled a shot just wide.
That represented the sum total of United's threat to the Valencia goal, although, with Rio Ferdinand back to reinforce their own rearguard, they looked far more secure than in recent weeks and restricted their hosts to general pressure rather than clear-cut opportunities.
Their best came through a rare mistake from Edwin van der Sar, who completely failed to cut out Alejandro Dominguez's right-wing cross.
Roberto Soldado seemed to be waiting more in hope than expectation of getting his head on the ball and it showed as he reacted to what was actually a clear sight of goal far too slowly and turned it over.
Pablo Hernandez was Valencia's danger-man, though, fizzing a couple of crosses into dangerous areas before the break, then firing wide of the far-post immediately after it after he had cut in from his right-wing station.
Ferguson needed his side to make better use of their possession.
Park Ji-sung was lucky to survive into the second period after receiving a rocket from his manager for giving the ball away rather too often.
Berbatov is rarely guilty of that offence and after bursting past David Navarro failed to take his second opportunity of the game when Cesar Sanchez made an important feet-first save, even if the Bulgarian had been trying to score from an acute angle.
With a combined debt of £1.136billion - building work on a new stadium that started in 2007 has stopped completely and David Villa and David Silva were sold to Barcelona and Manchester City in the summer to ease Valencia's financial situation - the winning prize money would come in handy.
Neither side looked like getting one, or deserved to given the paucity of chances.
The introduction of Manuel Fernandes did trigger an improvement from Valencia.
Van der Sar needed to push away the midfielder's long-range effort before Soldado came close to turning home Aritz Aduriz's cross with a desperate attempt at a diving header.
It looked for all the world like ending in a stalemate. Hernandez had other ideas.