Rhinos remain on course to retain the trophy they won at Wembley last August following a gritty 24-6 success away to Hull last night.
Despite being without six first-choice players through injury, Rhinos produced a commanding display which saw them lead 24-0 before the home team scored a late consolation try.
McDermott praised restored half-backs Kevin Sinfield and Rob Burrow for the way they ran the game in difficult conditions.
Burrow had been left out for last Sunday’s league clash with Hull, when Sinfield started among the substitutes.
“Both the halves managed the game really well,” McDermott said. “The game came down to management of the weather.
“I don’t think Hull lacked any effort or game plan, it was simply down to weather.”
Sinfield kicked for goal from five penalties and McDermott said: “He makes his own decisions.
“It was always going to be about points on the board.
“We were fortunate we got that early try and then a penalty to go 8-0 up and then they were in chase mode.”
The coach was also delighted with his side’s defence, describing try-saving tackles by Brett Delaney and Zak Hardaker in the second half as crucial moments in the tie.
He added: “I don’t think it was perfect game-management from us in the second half.
“I thought Hull kicked better than us in that second half.
Hull coach Lee Radford paid tribute to Sinfield
“The sooner he retires and goes to rugby union, the better I’ll sleep at night,” Radford said. “He kicked us all over the field.”
Radford - whose team visit Wakefield Trinity Wildcats in First Utility Super League on Wednesday - apologised to Hull’s fans for their performance.
He said: “I am unbelievably frustrated. We just haven’t been good enough over the 160-minute period. Our execution and skill set wasn’t good enough to beat a team like Leeds.”