Sinfield concedes there were few positives to draw from England's 34-6 quarter-final triumph over a struggling French team at Wigan but remains confident they will improve sufficiently to get past the Kiwis in Saturday's first semi-final at Wembley.
"I'm disappointed, but a win's a win," the Leeds half-back said. "I wouldn't say it's concerning. We won 34-6 in the end.
"I don't think the result was ever in doubt. I'm just disappointed with our intensity. I felt we were a little bit off from what we've been in the group stages.
"Hopefully it's a kick up the backside. Thankfully it wasn't in the semi because we would have probably copped a heavy scoreline against us."
England's stuttering performance was in sharp contrast to the slick displays by Australia and New Zealand that saw them ease effortlessly into the last four.
France, who only reached the knockout stages thanks to an opening 9-8 win over Papua New Guinea, briefly threatened to pull off their first victory over England for 32 years when centre Vincent Duport scored their third try of the tournament after only four minutes.
England's initial response was breathtaking as they hit their visitors with four tries from wingmen Ryan Hall and Josh Charnley in an 18-minute purple patch.
Full-back Sam Tomkins, appearing at the DW Stadium for the last time ahead of his move to Auckland, supplied the passes for the first two touchdowns while centres Kallum Watkins and Leroy Cudjoe showed touches of class in enabling their wingers to double their tally.
It was an especially sweet moment for Charnley, one of five Wigan men appearing on their home ground who made the most of his recall, while the prolific Hall extended his lead in both the World Cup and England scoring charts with his eighth try of the tournament and his 21st for his country.
But that was as good as it got for Steve McNamara's men, who laboured for the remaining 55 minutes , adding just two further tries through back-row forwards Brett Ferres and Sean O'Loughlin, with Sinfield taking his goal tally to five from six attempts.
It was a familiar pattern for England, who played Australia off the park in the first quarter of their opening match and destroyed Ireland and Fiji with 20-minute scoring bursts.
"We can't do that next week, we need to put an 80 together," admitted Sinfield, who has been impressed with the way the Kiwis have piled up 186 points in their four matches so far.
"We're disappointed with what we've dished up but we're through to the semi-finals of the World Cup. We've a whole host of things to fix up and I'm sure we'll be a whole lot better next week. We have to be.
"We know how well drilled the Kiwis are and what a great side they've looked so far.
"I don't think they've got a weak link. They've a big strong forward pack, exciting backs and two very good halves as well.
"It's a tough proposition that is in front of us but we've got it within our squad to be good enough next week. Like I say, we need to fix one or two things up.
"We made a whole load of errors which we were able to defend. Whether we'd be able to do that next week, I'm not sure.
"We certainly can't cough that much ball up.
"We've seen how well they can play. I don't think we've quite seen best of us yet and there will be no better stage to do it next week."
- Sports & Recreation