The Whites were again missing a host of senior players and Bielsa could name only one senior operator on the bench, 15-year-old Archie Gray joining seven other Under 23s among the substitutes.
Bielsa had to use two of his young replacements in the first half due to injuries sustained simultaneously by Adam Forshaw and Junior Firpo. Against that backdrop, Leeds defied adversity and a strong Hammers outfit to take three points. Jack Harrison left with the matchball having scored all three goals, while VAR ruled out a Mateusz Klich strike and Raphinha struck the post.
Victory pushed Leeds up to 15th place, above Everton, and nine points clear of the drop zone.
The players' efforts allowed them to show the best of themselves and earned praise from their head coach.
"I think the word you used [bravery] is one of the ones that best defines the team today," said Bielsa.
"I think it was a triumph for the players. Each of them things did things that indicated a great desire to win. The three forwards complemented themselves in a harmonious way. Raphinha improved James and Harrison with the types of balls he gave them. Harrison scored three goals, so that exempts me from having to make commentary and James opened up spaces constantly. It was a very, very big effort.
"I clearly observed that it was a game for each of the players. There was a determination, an implication in the search for victory that was very visible today. I think it's the biggest factor that the game today leaves. When a footballer puts so much effort into what they do, the virtues they possess come out easier. They're more visible. "
Bielsa welcomed Pascal Struijk and Rodrigo back to his squad after lengthy absences, but was once again without Patrick Bamford who was not risked at the London Stadium.
"He isn't injured but we thought it would be premature that he came back," said the Argentine.
"For example Rodrigo coming on is also linked to the fact that he hasn't competed for a long time. If he had come on in the first half the game would have been too long. That's why we split the time between him and [Lewis] Bate. One thing is to be healthy."
On a day when the North London derby was called off due to a Covid-19 case at Arsenal, a decision that drew criticism from Tottenham Hotspur, Bielsa was asked if Leeds applied for a postponement but said they did not meet the criteria to make such a request.
The Gunners were due to be without at least 15 first-teamers but at the time of the Premier League's decision to postpone the derby only Martin Ødegaard was known to have Covid-19. Injuries and the Africa Cup of Nations formed part of Arsenal's request, leading Spurs to release a strongly-worded statement.
It read: "The original intention of the guidance was to deal with player availability directly affected by Covid cases, resulting in depleted squads that when taken together with injuries would result in the club being unable to field a team. We do not believe it was the intent to deal with player availability unrelated to Covid.
“We may now be seeing the unintended consequences of this rule. It is important to have clarity and consistency on the application of the rule. Yet again fans have seen their plans disrupted at unacceptably short notice.”