Captain and stand-off Sinfield created four of his side’s six first-half tries, two of them with pinpoint kicks for wingmen Ryan Hall and Ben Jones-Bishop, to help the Rhinos avenge last year’s Wembley defeat by the Warriors.
The victory came just six weeks after Leeds suffered a 50-8 humiliation at home to Wigan and illustrated the new-found confidence running through their team.
“It feels great,” Sinfield said. “Five or six weeks ago we had 50 points put on us by the best side in the comp so to turn it around is awesome for us.
“I’ve got to give all our pack a big wrap. I’m just doing my job for the team. Our big men set a huge platform for us. They had a much tougher job than me.”
Sinfield admitted the Rhinos’ set out to nullify the threat of danger man Sam Tomkins, whose early failure to deal with Sinfield’s spiralling kick gifted Hall the opening try.
“Sam is the best player in the comp at the minute and we did a lot in our game plan to keep him quiet,” Sinfield added.
“A kick is only as good as its chase and our chase was aggressive and had so much desire to get down there.”
Leeds led 16-0 after 10 minutes and were 30-12 up after Jones-Bishop scored his second try but coach Brian McDermott admitted he could never relax, even after Sinfield’s 64th-minute drop goal put his side three scores in front once more.
“It was the smart thing to do but I didn’t breathe easily at any time throughout the game,” McDermott said.
“Wigan were white hot the last time we played and I don’t think they were far off today.
“They kept coming at us and, if our pack hadn’t been as tough as they were, we wouldn’t have got the job done.
“I also thought Danny McGuire was outstanding. They came at him but he was sensational defensively and kept probing away.”
Leeds, who have not won the Cup since 1999, will seek to end their wait when they meet the winners of tomorrow’s tie between Huddersfield and Warrington at Wembley on August 25.
Wigan coach Shaun Wane was left to lament his side’s worst performance of the season.
“The bad start didn’t help but we made too many errors throughout the game,” he said.
“A few in the first half were uncharacteristic.
“I said before the game the team that completes best would win and that’s what happened.
“It was our worst performance. We didn’t turn up today. We’ve defended all year better than that.
“But take nothing way from Leeds. They wanted it more which to me is gutting. They’ve some real warriors in their team.”
The Warriors are still top of Super League and Wane says his team will use their Cup exit as extra motivation to reach Old Trafford.
“We’ve just spoken about that in the dressing room,” he said.
“There are two ways of responding.
“But we won’t sulk and I’m expecting real change in attitude at London next week.”