Lita, borrowed from Premier League strugglers Swansea, provided the only quality moment of a desperate Championship clash with 14 minutes left.
The forward sent a searing drive which sped just inside the left post at Elland Road to earn the Blues only their second away win of the season.
On the occasion of his 40th birthday, Clark said: "The beer will certainly taste sweeter tonight, that's for sure. I have family and friends coming down and they were hoping I would get a good result because they know what I am like when we lose.
"They didn't want a soppy faced 40-year-old hanging around them."
Clark was delighted with his team and added: "The first half set the tone. We dictated the tempo and did what we set out to do by nullifying the crowd. Leeds came at us a bit more in the second half but the lads stood strong and defended well."