Bielsa's free-flowing Whites have passed the test of a tough looking first five fixtures with flying colours with former Championship title favourites Stoke City blitzed 3-1 at Elland Road on the opening weekend.
United then cruised to a 4-1 victory at Frank Lampard's well touted Derby County before recording a 2-0 win at home to plucky Rotherham United and then drawing 2-2 at recently relegated Swansea City.
Leeds then emphatically returned to winning ways with a 3-0 triumph at last Saturday's hosts Norwich City leaving the Whites top ahead of tonight's showdown with Middlesbrough who have also amassed four victories and a draw from their first five games.
Victory for either side this evening would send them three points clear heading into the international break and Bielsa recognises the importance of both the fixture and United's opponents even after just five games.
Asked if United were facing their toughest test yet, Bielsa said: "It’s difficult to make comparisons.
"Because when we played against Stoke or Swansea we had an opposition, an important team against us because they were a couple of months ago Premiership teams.
"It’s an important rival, opponent, no doubt about it. It’s going to be a very difficult, tough game.
"I don’t want to put classification between teams. But for me the next game is always the most difficult game. And in this case, this particular case we have many reasons to think that this coming game is the hardest one."
Asked when he would regard the Championship table as meaningful, Bielsa said: "The table is always important for us.
“The coming game on Friday is important by itself.
"It’s not important because we can be first, it’s important by the game itself.
“When I explain that the table is always important for us and at the same time I say we don’t look at the table so it looks like a contradiction, what I’m trying to explain the important thing is to finish the Championship in the best possible conditions or position.
"If we take each segment of the competition and if we make segmented conclusions we will be making a mistake.
“This conclusion I see in the media and the press taking the example of last season at the middle of the competition, Leeds were third or fourth in the table and at the end they finished 13th.
"The conclusion is not to get too enthusiastic right now.
"The idea is to keep doing what we doing until we reach our goal."