The new signing met a David Healy cross inside the area and took his time before hitting a low shot under Darlington keeper Bertrand Bossu.
Kevin Blackwell left it until the 57th minute to make any changes as Frazer Richardson replaced Gary Kelly and Gylfi Einarsson replaced scorer Blake.
Leeds should have had a second goal but the referee missed a clear handball by Darlington defender Ryan Valentine inside his own penalty area.
Further replacements were made after 70 minutes with Paul Butler making way for Matthew Kilgallon and then Matthew Spring replaced Shaun Derry with Simon Walton, Danny Pugh and Michael Ricketts coming on later.
It was a comfortable 1-0 win for Leeds in the end with only Clarke Carlisle and Dan Harding missing out on the night.
Leeds: Bennett, Kelly (Richardson 57), Gregan, Butler (Kilgallon 71), Crainey, Wright (Pugh 84), Bakke (Walton 84), Derry (Spring 78), Johnson, Blake (Einarsson 57), Healy (Ricketts 87).
Subs not used: Carlisle, Harding.